I have the same exact issue you have. It's not night shift but with having clients in between different times, its hard to get a meal in and when I actually have the chance to get one in, I am extremely tired and my appetite is there but I feel like I have to force myself to eat at times. I use multi vitamins (iForce Athletic-Multi) for the b-12 which one of it's benefits is helping increase appetite and energy. Although many people find the absorption rate a lot faster injecting it. I also do cardio which IMO helps me out with increasing my appetite after 30 mins or more on the stair master.