PredniSONE Januvia 100mg, Adrenal Glands, Vitiman, Term Consequences, Grave Disease

I have been on prednisone for about 7 months for RA..Started with 20mg, went to 10, 5, and now down to 2.5.. Trying to wean off it, but all the joint pain, and swelling coming back. I have tried other meds for the arthritis, but nothing stops the pain like the prednisone. I am almost on my last dose, 2.5mg every three days, and the pain is almost more than I can bear in my joints (feet, ankles, wrists, fingers) What I would like to know is this. If I stay on 2.5mg for a long period of time, maybe until I die, ( I'm 67 female) what will be the long term consequences? Also how long does the prednisone stay in your system, and how long do the withdrawal sides effects last, after the last dose. I want desperately to get off the drug, but very hesitant.. I am also on synthroid, have been for 25yrs, Januvia 100mg, enalapril 5mgs, and simvastatin 20mgs...Take VitaminD 50,000units once a month, Calcium 500 - magnesium 250 and Vitiman B12 1000mg daily. Am hoping maybe if I stay on the prednisone if necessary that the vitamins will counteract to bone loss. Will 2.5mg of pred. have that much toxicity on the body.. (Thyroid med is .125mg. diagnosed with Grave disease 25-30 yrs ago...everything is under control now. The only side effects that I noticeably see with the pred. is a small weight gain, and seems like I break out a little on my face nothing really bad. I am a mentally very strong person, so I don't know about the psychological effects..Don't seem to have any.. Please try and answer my questions...I feel like I am between a rock and a hard place...I am very uncertain what to do..My Doctor said that if I really can't stand to pain, maybe I should stay on the 2.5mg pred...Doesn't really want me too, but if there is no alternative......Also will it have a bad effect on my adrenal glands.... Thank you so much for listening