Help me build muscle?(i'm a girl)?!

I'm 5'2 and around 100 pounds. I know i'm tiny.. i recently lost alot of weight but did it the wrong way. (i weighed 125) I did too much cardio which took away all my muscle (but i did have fat on me i ate very unhealthy lol).... I'm an athlete (i skate) and i workout quite a bit..I also do plyometrics. i'm going to start weight training a little.I cant hit the gym EVERYDAY because i do have my long skating practices...but i do do abs and leg routines in my room on days i dont go. Also plyometrics once or twice a week. When i go to the gym i do interval runs.. should i lay off the steady cardio? I stick to a healthy diet (oats whole grains low fat yogurts and cottage cheese fruits veggies chicken salmon fishes natural peanut butter etc) well i'm looking for how much should i be eating and what? My coach says peanut butter toast with banana on top is a good pre workout meal to build muscle? What about luna bars? I love these.. are these good? Maybe a luna protein for after a hard workout like plyo? Should i be eating alot more too? Hahaha sorry for all these questions :p i just need to know! thanks :)