Welcome aboard...
After reading your posting... I felt like I was hearing myself. I recently left working in a school... great place, kids were fantastic, families were familes, but I truly enjoyed their being. I had to leave due to personal reasons.
After leaving I mourned the kids, the "what's happening" with all of them. I have put on weight in my middle area... I attempt to work out and loose the motivation to other things which need to get done.
But, as young as you are, and free in your mind... my best advise is not to dwell on a thought "new years resolution". You tend to feel badly because you broke it.
Things that worked for me...
using a calendar in the kitchen - marking Mon., Wed, & thurs. as workout days...
Lots of motivational music...
Once you get in a habit your mind breaks that course it has been on for so long... you begin to correct bad habits all by yourself w/o "changing a thing". You see a difference, so you curb your appetite alone. You feel better mentally so you continue to workout.
Before you know it your life cycle is giving back!!!
Good Luck and welcome aboard!