This is actually good news because you're at a great age to start making big gains, if you get with a smart plan.
Important question for you: What, exactly, did you eat yesterday?
This article has a great list of foods to focus on, with some other good ideas about planning your diet:
I'm a fan of having younger guys set their foundation with basic bodyweight exercises before progressing to a free weight-focused program, so try:
Monday, Wednesday, and Friday
Squat 2x15 (No weight, keep both feet flat on the floor.)
Push-up 2x15 (On your toes, go until the chest almost touches the floor.)
Lunge 2x15 (Alternate legs, 1 rep left/1 rep right.)
Neutral-grip pull-up 2x15 (assisted if necessary. Could be substituted with inverted rows.)
Plank 2x15-count (Hold the top part of a push-up, on the toes, arms straight, keep the whole body straight. Count to 15.)
Burpee/squat thrust 2x15
As soon as that workout is "easy" (could take one week, could take six weeks, doesn't matter), there are any number of free weight-focused programs you can start on.