yeah, i tried gaining weight forever and ever but it never worked
i think the key is not just how much you eat..but WHAT you eat... watch your diet
what worked for me was eating every 3 hours... mostly these:
eggs ( i like 3 over easy), tuna sandwiches, wheat toast + cottage cheese, wheat toast + peanut butter, salad + cottage cheese, drink lots of milk, lots of water, oatmeal ... with raisins... etc. i concentrated on protein-loaded food.
i gained 5 lbs after the first week, and 5 more lbs the other.. and started working out , too.
then i had finals, barely slept any, barely ate any, but didnt lose that weight. ive always been a skinny build but that worked for me, im getting back in the routine right now. hope this helps!
edit: i had a shake everyday, too (20g), and my dinner every night was either chicken or beef so that helped alot, also. try to get atleast ONE gram of protein for 1 pound of your weight!!!