Weight Gain Help!!

bubbles • loving every second
So I'm a small person, and I've lost an unhealthy amount of weight for my size. I'm 5'3 and was 135lbs 6months ago. As of yesterday, I'm down to 111lbs. My eating habits haven't changed too drastically, but I stopped taking my anxiety medicine. Mostly, everything is the same as usual with my eating. I don't exercise. How can I put some weight back on?