Arthritis? I don't understand.

I'm 17 and my doctor just told me I have degenerative rheumatoid arthritis in my tmj joint/ jaw bones or whatever. Can someone explain what these are? All I know from her telling me is that the constant pain I feel probably won't go away unless I take medication or something like that.

She says I've probably had it since I was 13 (the first time I told her I was having jaw pains but her and all my family ruled it out as growing pains at the time)

I've never felt so sad in my life. I can barely eat or speak without being in pain and I try my best not to let it show because I know all my friends and family will just tell me it's not that bad and to suck it up. Knowing now that this is going to be permanent I just feel so done with everything rn.

Thanks for the clarification ladies ❤️😔