> I could not overeat to save my life
You are likely eating the wrong foods. It is _highly individual_ what kind of food can people eat in large caloric quantities. Start calorie tracking and experimenting more, you can figure this out. Some people do well with oatmeal (tastes like soggy sawdust to me), some with various nuts (peanut butter is a fitness industry staple), others make themselves milkshakes etc etc.
Progressive overload is key here, don't just expect to start eating 4000kcal/day, it is not going to happen (and would not be productive anyway).
> I cannot concentrate with a meal in my stomach
Same here. I feel like eating makes me lose about 10 IQ points, not great (though I am at a place in life where I can make this sacrifice). Maybe more sugar would be helpful here.
You may also find the /r/gainit subreddit englightening.