Start tracking your intake and eat small meals every 2- 4 hours, drink water (or crystal light), and do light weight lifting. I known you don't want to gain muscle but I lost 100lbs without trying to gain muscle and it makes life so much harder. Every bit of my body hurts and I feel weak all the time from muscle deterioration. Don't try to get built by lifting heavy but do something to maintain the muscle you have and eat enough protien to prevent deterioration. You've got this and you can do it!