Dude, eat more. That's the secret, not even kidding. Not gaining weight in 8 months means you're not eating enough to grow. As someone else said, it doesn't matter what you eat as much as how much you eat. I can eat only chicken and brocolli but get fat if I eat 5000 calories of it (which is pretty hard to do), which is why many people who eat "healthy" foods don't get fat: they're not calorie dense. It's not that the chicken and rice and veggies are magic foods, it's just really hard to eat so much of it that you get fat unless you force feed yourself.
I mean, I've dropped almost 30 pounds before eating McDonalds 2-3 times a week. It's about calories ingested, not necessarily where those calories came from. No I don't recommend doing the McDonalds thing but I knew what I was doing calorie-wise and wanted some mcdoubles dammit.
Back in the day I thought I was eating a lot, all I ate was big bowls of chicken and rice and I was always full. Turns out it wasn't even 3000 calories once I took the time to legitimately track it.
Stop looking for "diets and nutritions", whatever that last thing means, and just eat more. That's it.
Track your calories for a few days. Just worry about overall calories to start with if you don't want to track every macro. If all you eat is chicken and rice, just look up those 2 foods and weigh/measure your food next time before you cook it and use that to estimate every other time. Takes like 5 minutes the first time then 5 seconds every meal.