Right now I am 5'9 and weigh 140 pounds (I am 22 years old if that matters). I've always been pretty skinny but this is the lowest I've been since probably early high school. At this time last summer, I weighed 155 pounds, which was probably my peak. I drank a ton of soda, didn't eat any vegetables or fruits, and ate a lot of junk food like potato chips. Despite all that, I was still fairly skinny. I think its just really hard for me to gain weight.

Since that time, I've made changes toward paleo and lost weight. Firstly I gave up soda. Then in February I went about 80% paleo. Then in May I went 99% paleo and I've never been better. My acne has cleared up almost completely. I'm in the best shape in my life, routinely playing basketball and doing bodyweight exercises. Yet I feel like I should weigh more.

Browsing some of the weight gain threads here, I see recommendations to eat certain carbs like potatoes and sweet potatoes. I would like to do this, but I know that eating potatoes causes my acne to flare up. It isn't nearly as bad as eating grains, but having a serving of mashed potatoes or a baked potato will cause a pimple or two. I haven't experimented with sweet potatoes yet so that might be a place to start.

I tried drinking a gallon of milk of day for week. It worked; I gained about 3 pounds but I don't think my body can digest all that milk. My BMs became loose and liquidy. But when I generally eat dairy (milk, greek yogurt, cheese) I don't seem to have any negative reactions.

What can I do to gain weight? I've been eating about 2500 calories per day (60% fat, 30% protein, 10% carbs) since going 99% paleo. I cook everything in coconut oil and douse my veggies in melted butter. I realize that I can gain weight eating carbs, but I'm worried my acne flaring up.