Cyst on 5year old - at the knee joint

My 5 1/2 year old son has had two bakers cysts removed - he has now got another lump and is suffering with a lot of pain, somedays he cannot put his weight on his leg (he is really skinny).  The specialist says it is not a bakers cyst but another cyst that will once again have to be operated on to remove it, but we have got to see the specialist in six months because he is hoping the cyst will have moved further down the leg making it easier to operate.  In the meantime my son has got to keep active and put up with the pain.  Is there anything I can do to help my son other than giving him Nurofen medicine to take away the pain.  My son is not a child who makes a fuss, so when he is crying with pain I know that he is not putting it on.