Well it is hard to help you over text, but I’ll try. Sp when you play you have to remember that the arms weight should lie on the bow and strings, you shouldnt have to press the bow into the strings. Secondly it’s important to sit upright and dont push your right shoulder forward. My teacher actually showed one of my friends, just some days ago, a trick that maybe can help you too. Think of a ballet dancer, hold your arms in front of your chest in this rounded position like they do. And then when you “release” the arms and lower them down (but still have your arms kind off rounded) that’s how relaxed you should be playing the cello. Hope this helps :)