Gaining Weight

Hi!! I'm 5' 1" & only 93 pounds 😕 I lost 7 more pounds when I was trying to GAIN weight! Does anyone have any good ideas on how to gain healthy weight? I don't want to do a LOT of running because that is what makes me lose a lot of weight. also, I know I am underweight, my doctor has told me plenty of times but I just can't gain weight ! Any suggestions are appreciated and welcome :)