Why do i begin to gain weight as i stand too long on my feet at work?!

Why do i begin to gain weight as i stand too long on my feet at work?

I started working as a sales which is a position that requires me to stand on my feet for 8 hrs, on the weekday from 12pm-8pm (including one hour breaktime when i can sit and eat my lunch).

I Thought standing could burn more calories than sitting? i just keep gaining weight since i started to work. I haven;t eaten excessively but just a bit more than i used to eat but i guess that offsets the amount of energy required by standing.
I always come home afterwork with my feet feeling painful and the muscles of my legs felt very heavy. could the heavy feeling atrribute to the weight gain?
I also have a later schedule of eating ever since i started my job. I usually finish my last meal of the day at 10pm, then i'd go to bed at 2-3ish am and wake up at 10am.
???????????

maybe you need more energy because you have to stand for so long. or maybe you have anxeity for this new job. maybe your not eating as healthy as you were when you were at home.

your legs aren't used to standing all the time, and are building up new muscles. the weight gain may also be water weight.

also since you do start your job at a different time, maybe your body needs to adjust, and the caloric balance needs to be adjusted as your body get's used to the new routine.