Tips and tricks to gain weight

I need help! I know people are probably going to think I’m crazy but I really need help on gaining 20 lbs. I weigh 105 now skin and bones. I have a super fast metabolism so “just eating a lot” doesn’t help at all. It just makes me sick. What are some good workouts that’ll help me gain weight like in muscle? Since my body can’t seem to hold onto fat I need to gain something somehow. I’ve been drinking ensure protein drinks and I’ve noticed my biceps are getting bigger but I’m also looking for ways to increase my thighs and butt. Any advice would be appreciated!! Thanks in advance.