Weight gain!

So I’m 19 and in the last few months I’ve lost 10 pounds without even trying and I want to gain it back! I felt comfortable at 120 and I want to be happy with myself again. I don’t know how I lost all this weight maybe stress or anxiety since it has spiked recently. But I was just curious if y’all had any tips for gaining weight and I can’t just eat everything cause I have gerd so my stomach is sensitive . But ya any advice to gain weight please send it my way!