I've been underweight my whole life. My wrists are small enough I can touch my thumb and middle finger together when I wrapped my hand around it. Of course, smoking cigarettes and having a feast/famine eating routine most my life has always upset any real attempts to gain weight in a good way. Even when I was in weight training (and basically eating whatever junk food I liked, as has pretty much been my way my whole life), I couldn't really bulk up. My favorite food is pasta, FFS. Been eating it by the pound probably my whole life. Even the parts of my body that "train well" (my legs) didn't really get fuller. They just got rip cord lean. My chest actually filled out doing bench press a bit. Meanwhile, my shoulders, forearms and lower arms got leaner too, but never any bigger. Now that I'm getting older and totally inactive, I'm developing a gut over the almost sixpack I had. But the arms/shoulders? Still look like the scrawny arms of a teenager.
While you hopefully don't have the lifestyle habits I do, it sounds like you have a similar metabolism. This:
The problem seems to partly be volume of food, I get full very quickly so often only have 2 meals a day (eating a often breakfast makes me feel queezy).
Is me exactly. I can't eat breakfast in the first hour or two of waking up, or I feel nauseous. So my first meal is typically lunch, then a large dinner. Unlike you, I don't get full quickly. When my body is ready to eat, I can eat enough that puts far larger guys to shame. That bit of pride being said, it's
not a healthy pattern for the body. I believe it's one way to end up diabetic, is the feast/famine cycle. I suspect the reason I've been putting on weight the last few years is I'm working and getting a more consistent diet.
One thing to remember is that muscle doesn't become fat. Fat just goes on top of it. So if you spend some time developing a good core while focusing on a high calorie, high carbohydrate diet, and your body hopefully works with you, you can fill out without necessarily having to go to the gym to work at it for the rest of your life.
The key is probably going to be your diet. You're going to have to eat more than you're burning off, consistently, for months. When actors need to transform themselves for a role, they eat in truly mind blowing amounts. You don't have to go that extreme, but there are some tips you can take.
For example, snacking. I don't really do it. I tend to only eat when I'm truly hungry, because I enjoy the feeling of being satiated. But it's what's kept my metabolism so high strung all these years. So start carrying some high calorie, high fat snacks with you. Eat something every hour, as much as you can stomach. Having a touchy stomach myself, I know that sounds pretty unappealing. But I find after the first 3 or so hours from waking up, my appetite picks up. Whether you do breakfast or brunch or lunch or whatever, start the snacks around that time.
Because maybe what you're needing most isn't necessarily more food, it's rewiring your metabolism to store fat differently. That, combined with meals aimed at calorie gain (meat, potatoes, pasta, breads, cheeses, sugars, fats) and working out should give you some noticeable results. I wouldn't go hog wild on complete junk food though, there's a lot of things processed junk food that you don't want to be eating in large quantities and will probably leave you feeling unhealthier.
Just remember. You've got to be eating more than you're burning off, and so for guys like us that might mean feeling uncomfortable full throughout the day, since we're so used to running on fumes because that's how we've taught ourselves it's time to eat something.