Could be a lot of things. could be a UCL tear but also could be a forearm strain or just some soreness. how Long is is going on now? the best if you have such a pain is to take two weeks off throwing (and other forearm taxing stuff) and then slowly start throwing again. if it still hurts then go to the doctor.
I would rest my arm until the appointment and wait for the results, that is not easy to do but you don't have any choice, we aren't doctors here and even if we were we could only guess without seeing your arm.
People recover fully from TJ all the time but it will likely cost you about 18 months of playing time (at least until you are back to full strength and have your game pitching ability back, you might be able to step on the Mound in games earlier than that but don't expect to be at your prior Level right away - not just Velo but also command and feel for Spinning offspeed stuff).