I have just finished 7 days in a thumb spica for tendonitis. it's still not better. what do i do next?

If it is for : Dequervains or tendinitis of the first dorsal compartment then nsaids corticosteroid injection and avoidance of a rigid thumb spica but instead using a softer splint such as a comfort cool generally yields a good result in most cases , rarely these need surgery. Often the treatment goes splint then meds then injection but i find that doing all 3 concurrently works better and 7 days is not enough.

Nsaids: You likely have a trigger finger. Nsaids, steroid by mouth, injection of steroid or surgery can improve the problem. Consult a hand surgeon for the most appropriate treatment in your case.