It just requires that you eat more that you need. You have to get used to stuffing yourself. It helps if you really like having a swollen belly, so stretch your belly by eating even after you feel full. --HXTP
It is natural for your age group (under 30 yrs old) to have a fast metabolism. Eat foods with a high calorie count. Just google "high calorie foods".
Starve yourself. You'll go into starvation mode and that means your metabolism will slow to a crawl.
I had the same problem my doctor prescribed me cyproheptadine it builds your appetite
yes, seek out the wise ones known as ben and jerry
You probably fidget, if so, learn to hold still.
Have you tried drinking a quart of eggnog a day. That's what the doctor had me give my Mom for this and it worked. Good luck.