Coffee?

So to start off I've always been on the thin side it is incredibly hard to gain weight no matter how much I eat! I guess that's where the stress kicks in I start losing hope and I'm sick of always seeing family and the first thing they say is omg your so skinny!👊🏼 ugh it pisses me off to the point where my husband notices how down it gets me he knows how much I struggle with it... anyways I spoke with my doctor my past appointment she said I should try coffee i am not a coffee drinker..she said it should help... she also advised ice cream even olive oil on salads.... I've gained 8 pounds since my last appointment I was a little underweight for my height and age .... I've always had this struggle but not it's even more stressful because I'm pregnant, although the baby is healthy and growing as he should be! It's just is anyone going through this or can relate? What do you do to gain the extra weight besides coffee? I know as long as the baby is growing and healthy . But I'm speaking in general like I struggle with this whole weight gaining any tips for after baby when I no longer have the extra pounds to make my weight be where it should ?