Nightshift in itself is bad its not you. Night shift leads to an increase in cortisol level night shift is very lonely leading to more stress and how do you cope with that by eating alot, Plus security guard job is kinda sedentary unless you patrol alot. My advice to you find a new shift during the day less cortisol more social life more happiness less food. If you cant find a daytime job quickly in the mean time you can do little changes to help you . Take your vitamin d supplement please and get a lot of uninterrupted sleep try to get enough sun during ur days off have a good social support.