How Can I Have Mixed Connective Tissue Disease After A Heart Transplant While On Immunosuppressants, And Is My Transplanted Heart At Risk?

I had a heart transplant March 21, 2015 and I was just diagnosed with Mixed Connective Tissue Disease. They had said I couldn t get an auto immune disease because my immune system is so suppressed by use of 2 medications called Everolimus (Zortress) and Tacrolimus (Prograf) as well as 2.5 mg of prednisone daily. My question is how is my heart safe if my immune system is attacking my connective tissues and muscles? I am very worried and having trouble with shortness of breath and fatigue. I am trying to get in with a new rheumatologist, but that can take around 3 months and by then it may be too damaged to help me. Can you please tell,ore about this disease and my risks? Thank you