Without really knowing you, my general advice for a not terribly underweight but understrong/under gainzZz'd guy who is 19 years old like you is to reset your weights so form is good. Do TM as written or on a split like I've talked about on my blog about it. Sleep 8 hours a night because you fucking can and don't binge on crap food because you're eating "big".
You'll have to eat more than you want to, but I tend to think that eating like a bodybuilder, minus all the stupid broscience, is a good mindset to have. You'll just have to titrate the amount of food up so that you're gaining weight.
Also, for the girls- if you're relying on your abs to get you laid you're not doing it right IMO. Think about it, you're hoping to that a chick notices you have abs and is so into abs she either doesn't care what you say to her or is only going to let you talk to her because you have them. I haven't met a lot of women like that- certainly not ones I want to expend any resources on (time, money, emotional investment). Just be yourself, be confident about who you are, and don't be the over invested one. Confident people with high self worth don't do that, abs or not and it's been my experience that they really don't care.