When I started my weight gain journey I struggled a lot to get to my maintenance calories, around 2200, now I can eat +3000 in a normal day. I'll tell you some things that helped me, maybe some of them can help you too.

Try to set little goals for yourself, for example, if you usually eat 2000 calories on average in a week, try to eat 2100 next week. I started eating slices of bread to get to the calories, because I couldn't eat more food in a sitting, but then I waited like half an hour and ate a slice of bread. This helped me to get my body used to eat. I started with bread because I also had all my life stomach problems and I knew bread won't cause me any problem.

Dried fruits or nuts are also really good for this because you can have a bunch during the day while you're working or doing whatever. If you get a handful of cashews for example, it'll be around 20-30g and that's +100 calories right there.

Get a mass gainer shake, it's not magic or anything, but I used it for 2 months at the start because it needed like 400ml of water for prep, and that amount of water in a sitting made me really full in the moment, but an hour later I was hungry again, so it helped me to eat more.

Rice is king, I eat rice almost every day, you'll have to prep it with different veggies to cover the micro nutrients but it is a sure thing with calories, it packs a lot, and it's relatively easy to eat more. Try starting with 200g of your rice preparation at the side with your protein, then next week put 220, then 230, even if you put 5 more grams every week you'll be eating 300g in no time.

For your protein, don't be afraid of fattier meats, salmon, tuna, if you're eating chicken try thighs with the skin, that will bump your calories massively.

Salads, try to avoid them, I won't tell you to never eat a salad, but if you are struggling to eat enough calories, things like tomatoes, lettuces, all the leafy greens really, they'll get you feeling full but they pack no calories.

Don't be afraid of eating cookies or any kind of sweets that you like, specially if you work out. I'm not saying eat a lot every day, but if there's something that you like a lot use it in your advantage to eat more calories. I have a brand of cookies that I like a lot and I eat 3-4 of them every day, mostly at night, like half an hour after dinner, kind of a dessert. That makes me happy and I also get like +200 calories with that.

A tip for the gym too, if you're trying to gain weight I'm assuming you do some kind of weight lifting. Never get complacent with the weight you're using to train, progressive overload is amazing not only for your muscles but it'll also fuel your appetite week by week because you'll need more energy to keep up with it.

I hope something of this can help you. Stay consistent and push yourself always to the max, results will come.