3 month tfcc tear after being splinted and injected still is painful when bearing weight, what's next?

Tfcc tear: If you have not responded to conservative treatment you should see a hand surgeon about possible arthroscopy and/or surgery.

TFCC Tear: Some tfcc tears will heal, and some won't. Depends on type, location, and maybe most importantly the blood supply. Usually 3 months with adequate rest is long enough to know. Next step is typically arthroscopy. Talk it over with your doctor. Good luck.

Hand surgeon: Certainly would see a hand surgeon for this. Some of further treatment will depend on your response to the injection. If you had the wrist joint injected and at the very least got transient improvement that is at least a good sign of where your pain is arising. If so, then a hand surgeon might consider a surgery which would probably be at the minimum a wrist scope to assess the tfcc.

Test / Surgery: If no studies done, a routine x-ray followed by a triple arthogram with or without mri. If confirms clinical findings then an arthroscopic evaluation and debridement (shaving) vs. Repair should be entertained. It sounds like in your situation, that conservative care has been exhausted.