So, you're confirming that you are in fact anorexic?
I can tell you, from experience, it's not a disorder that you can't rid yourself from, just because you're tired of having it. It's a continuous, daily struggle.
A few options if you want to get better are therapy, counseling, or rehab. They all have different names, but are essentially the same on some level.
EDIT: These people that answered are obviously idiots and completely ignorant to the illness. "Eating a cheeseburger" isn't a cure. Fucking morons.
EDIT: Okay, I just read your additional details. You want to gain weight, but are unsure how. Honestly, you're probably fine where you're at. If you insist, to please yourself and mom, though, I can tell you that it may be harder than you think. You're one of those people blessed with a fast metabolism
, I'm guessing. Enjoy it! When you're much older, you'll wish you still had it.