Is there anything I can eat to gain weight quick without hurting my stomach?

I'm a diabetic and a couple of months ago I went trough a hard time with my glucose numbers and ended up losing 7 pounds cause of it, if I could eat the things I used to eat before getting diagnosed with mild chronic gastritis I would have recovered some of those pounds but since I'm following a diet I haven't gained a single pound in the last 3 months, it is really frustrating cause I was already skinny when I was 160 lbs cause I'm 6" tall but now with 153 lbs I look malnourished.