How can I gain healthy weight?

I used to weigh 110 before about a year ago and I've been going to the gym a couple times, now I weigh 91 pounds but I look way too skinny and I'd like to gain more weight but look fit, I've had family issues going on and I haven't been eating the same either because I've been too sad to but I don't starve myself I just eat a little.
How can I gain healthy weight?
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