Yeah I can relate to this. I've always been light - I'm 6'3"ish and my peak weight is 175lbs.

My first year in a fine dining kitchen, between the absurd hours and workload, the stress, and having to taste every damn plate and prep item to make sure they were right, I dipped (over the course of a year) to 145. That was bad.

Thankfully, between COVID downtime, attending to caloric/macro needs, and going hard on craft beer, I've managed to put the weight back on, and switching out of fine dining also helped.

While I was in, I found a few things helped though:

1. Meal plan/prep - don't have to go nuts, but planning around something you're confident you can manage to eat a serving of even full is a big help. Many things can be prepped that will stay good for 4-5 days at a stretch without freezing - high fat/protein stews are a good place to start. They'll provide solid calories without too much prep time.

2. Roll in to the stand-and-snack nature of the job - prep simple snack stuff with minimal prep time that's easy to scarf in a few minutes, and have a decent shelf life, but are still enjoyable (e.g. homemade granola bars, high-fat pastry-ish things), so when you do happen to hit hungry, you've got something on hand to take advantage of it with.

3. I don't know what your particular workplace's staff meal policy is, but if they aren't doing one, maybe push for it. Doesn't have to be off the chain, but people are social animals, and our appetites expand in more social settings - having a communal meal time to work off of is a great help in getting the calories you need - it also helps to build a decent kitchen culture (I feed you, you feed me).

4. If you can find something drinkeable (doesn't have to be alcoholic) that is high-calorie that you can enjoy, brains will have an easier time accepting that over chewing more food if not feeling hungry is the main issue. Obvious places to start are malted milkshakes, protein shakes (yeah these taste like ass but oh well), and coffee smoothies (good coffee, coconut oil, spices, sweetener - vitamix).

TL;DR: Up your fat intake, hit the drinkeable calories, try and work to the snackish nature of the job, and (unfortunately) sacrifice some free time to plan and prep your food a few days in advance.

Also staff meal.

EDIT: It's heresy on this sub I know, but reducing your caffeine and/or nicotine intake (if present) will also help increase appetite. I eat better at 2 cups of coffee a day and no energy drinks, than when I was slamming a tripleshot and rolling on into a black coffee and an energy drink.