autoimmune problem developing during pregnancy

Hi, I am currently 36 Weeks pregnant and I was having some weird joint pain and inflammation occur in my elbow and my doctor thought I had an infection and told me if it got red to go to the er. Well it got red and even more swollen and couldnt move it, went to er, they couldnt find an infection, and they gave me percocet for pain. Well, next day my other elbow became swollen, severely painful and red in the same exact spot and I couldnt move it either. So I stopped the antibiotics and made a recheck appt with my doctor. Third day, my knee did the same exact thing as my elbows and I couldnt move and I tried Tylenol, nothing. Tried percocet, nothing. Finally the day of my appt I told my doctor its worse and I thought I was loosing my mind and he confirmed that I wasnt. He left me in the exam room to go talk to a joint doctor. He comes back in and tells me he is prescribing me Prednisone which is a steroid because they think my immune system is attacking my joints instead of the small cough that I have. He didnt give me a solid answer when I asked him if it was just gestational or not. All he said was he hoped that it was because of the cough otherwise there would have to be further testing for rheumatoid arthritis and I'm ONLY 21 YEARS OLD! Has anyone else had this happen to them and if so, did it go away after you delivered?! I hate the side effects of this medicine and I do NOT want to have to keep taking it :