Loss of Abdominal Muscles?

Hey all. I seem to have lost my abdominal muscles. I have hyperthyroidism and I did have an episode where I lost about 15 lbs of muscle when my condition was severe, but that was years ago. I notice now that my abdominal muscles don't hold my stomach in, meaning, I feel very bloated in that section. So I try and work it out. It hurts as I do it, but the next day, it is not sore at all! I've tried different abdominal exercises as well and they just don't seem to work or help.

Does this problem sound familiar to anyone? Does anyone have ANY suggestions? Thank you so much!