I have taking chair yoga for 5 yrs now and I do have that same issue. It is always the twists that hurt my left side mostly. I do not do complete twist or some of the warriors 1 and 2 down low. You do have to modify what works best with no pain. It has been great for me the stretches and relaxation. Keep it up just don't do what u can't. My instructor tells us that same thing and should be able to advise u.
One thing that I would like to ask, sometimes I bleed from the rectum after yoga twists if I over do and also when doing physical activity around the home. ex: yard work, cleaning, running the sweeper. Anyone else have this?