EXERCISE CHALLENGE Check In

I also have join the gym, I've been going now for the past two weeks and my body is sore as heck.  I had a personal trainer and your right it can get expensive so I join with some other guys at the gym to help me work out so far so good.  But I have another problem I WANT TO GAIN WEIGHT AND I CAN'T! My current weight is 132pounds; however I would like to gain 10-12 pounds but I can't for the life of me!  I eat like crazy at one point my weight was 140 which I was very pleased with then I release some dead weight which was my boyfriend and lost the weight.  Any advise?