How to gain weight for vegan who is lactose intolerant?

i am lactose intolerant and i want to become a vegan. i am 13, 5'6, 89 lbs. i want tobe at least 110 0r 120. I will eat meat but don't want to. I can't have any products with milk or i'll have diarreah(<-spelled wrong?). How do i gain? ++ i can't lift more than 5lbs. so muscle gain is out! Is there fat injections or a such thing as lipoimplantion? ++I can not eat anythiing with a trace of dairy!