Hey there,
I was transplanted a little over 4 months ago and I have absolutely no regrets. It is amazing how much better you feel immediately after surgery and it just keeps getting better. I as well well pretty active until the day I was transplanted but I didnt realize until afterwards how limited I was. I had very little pain post-op. If this is a major concern for you, please talk to your doctor to discuss pain management options. My center had a pain team doctor on its transplant service, and she adjusted my pain medication as needed. As for the rejection meds, after the first few weeks I havent really had any side effects. Occassionally I get the shakes, which are mild and only noticable to me, and my blood sugars are high from the prednisone, but other then that, no problems. The ability to breath and run around without problems totally outweights the side effects of the meds.
Good luck and if you have any questions please feel free to ask.