There's a lot of factors going on here, genetics, snacks etc... it's tough to just pick out one thing to change, and changing everything is just overwhelming, so the tendency is just to kinda forget about everything and perpetuate the cycle.

So I will tell you that sitting is the killer.

I used to work crappy retail jobs, with lots of snacks, terrible sleep, just an awful lifestyle. However, I was on my feet all 8 hours, so sometimes I even lost weight.

Now, when I have a decent office job, I have great sleep, I watch my diet, and I gain weight... just because I sit all day.

Invest in some really comfortable shoes, maybe with special gel or whatever, and try to do half your shift standing up. Then slowly move to doing your full shift standing up. It's not impossible. You're going to see results after two weeks, I promise.