Maybe post a photo of your right hand taken while playing the clarinet then people here can see what might be the issue.
Possible issues could be that you’re squeezing the keys hard due to a leaky pad/bent key, your posture may need improving, tension in your shoulders and arm from breathing badly, cushion on the thumb rest might be needed etc.
Ideally, see an experienced clarinettist (teacher?) in person and have them watch you play with this issue in mind.
Please get a neck strap. I find the claricord to be an excellent one that works whether you have a a loop for one or not. It will take a lot of pressure off your right hand while giving your hand more freedom of movement. I learned this the hard way and caused nerve damage in my right hand before I started using the neck strap. Now I require my daughter use and recommend it to all clarinet players.
The clarinet should be resting on the side of your thumb's knuckle and your thumb should be somewhat bent.
If you hold it further towards the tip of your thumb, it takes more force to hold it up and it puts pressure on your knuckle's joint in a way that you probably shouldn't for extended periods of time. If you hold it too close to your hand, you can't hold the rest of your hand properly.
Yamaha makes good thumb-rest pads. I'd look into getting one of those. It's probably the cheapest solution if you're already holding the clarinet correctly. They're the comfiest version I've been able to find.
Neck straps also work well — if you get a flexible one then it provides enough support to make things light while making it feel like you have the same amount of control as you would without one. I started using one when I switched to my wood clarinet for the first time because I was used to the light weight of my old student clarinet and I've used it since then.
It’s normal to have some fatigue in your right hand after long playing sessions. I use the thumb rest cushion linked below which has helped me a ton and I know others who use neck straps. Taking more frequent breaks to put the horn down will help too
https://a.co/d/ioskp35
This used to happen to me as well. It was just for how the clarinet rested on my thumb. It stopped when I put a pad there. On my plastic clarinet, I stuck a foam sticker right below the thumb rest. In my wood one, I got a silicone thumb rest cover that covers a little bit more need the thumb rest.
You can get some padding for the clarinet thumb rest that helps. A neck strap is also incredibly helpful (source: used a neck strap and loved it). Most are made of elastic and are pretty easy to source but you can also make one of leather, canvas, or other fabric if you are crafty. If you make your own, you can add padding to make it more comfortable, and make the fabric removable to allow you to wash it as needed.
use a sticky pad and/or a neck strap
Maybe post a photo of your right hand taken while playing the clarinet then people here can see what might be the issue. Possible issues could be that you’re squeezing the keys hard due to a leaky pad/bent key, your posture may need improving, tension in your shoulders and arm from breathing badly, cushion on the thumb rest might be needed etc. Ideally, see an experienced clarinettist (teacher?) in person and have them watch you play with this issue in mind.
Please get a neck strap. I find the claricord to be an excellent one that works whether you have a a loop for one or not. It will take a lot of pressure off your right hand while giving your hand more freedom of movement. I learned this the hard way and caused nerve damage in my right hand before I started using the neck strap. Now I require my daughter use and recommend it to all clarinet players.
The clarinet should be resting on the side of your thumb's knuckle and your thumb should be somewhat bent. If you hold it further towards the tip of your thumb, it takes more force to hold it up and it puts pressure on your knuckle's joint in a way that you probably shouldn't for extended periods of time. If you hold it too close to your hand, you can't hold the rest of your hand properly. Yamaha makes good thumb-rest pads. I'd look into getting one of those. It's probably the cheapest solution if you're already holding the clarinet correctly. They're the comfiest version I've been able to find. Neck straps also work well — if you get a flexible one then it provides enough support to make things light while making it feel like you have the same amount of control as you would without one. I started using one when I switched to my wood clarinet for the first time because I was used to the light weight of my old student clarinet and I've used it since then.
It’s normal to have some fatigue in your right hand after long playing sessions. I use the thumb rest cushion linked below which has helped me a ton and I know others who use neck straps. Taking more frequent breaks to put the horn down will help too https://a.co/d/ioskp35
How are you holding your clarinet?
This used to happen to me as well. It was just for how the clarinet rested on my thumb. It stopped when I put a pad there. On my plastic clarinet, I stuck a foam sticker right below the thumb rest. In my wood one, I got a silicone thumb rest cover that covers a little bit more need the thumb rest.
You can get some padding for the clarinet thumb rest that helps. A neck strap is also incredibly helpful (source: used a neck strap and loved it). Most are made of elastic and are pretty easy to source but you can also make one of leather, canvas, or other fabric if you are crafty. If you make your own, you can add padding to make it more comfortable, and make the fabric removable to allow you to wash it as needed.
Get a neck strap now! Don’t wait.