I've been there done that ... i was 5'7'' 85lbs (8th grade playing football at the time starting both ways)... skinny halocaust child that didn't eat anything. well i ate three times a day, maybe four, but i was inconsistent...
today i'm 5'9'' 132lbs (3-7% body fat) trying to become 145 all muscle...(3-6% BF)
i gained a lot of weight eating junk... which was bad... patatoes were bad and cheap, they made my heart valves very clogged. This reduced my mile times and cardio a lot... it nearly killed my long distance running, i could run 2 miles without a stress on my heart, now i cannot run 1/4 mile without 180 BPS (beats per minute)
i gained 20 lbs in four months eating a lot of bad food ( would not recommded it ) this 20 lbs was not good weight... so i became 5'8'' 105 in four months (while still growing from 5'7 85lbs)... this was to play football back when i was 9th grade ( started both ways that year RB(four back)WR/CB/S.... eating 5-6 small meals a day is a good start. no more than 2 egg whites/ day... adjust so you can eat 2200 cal a day then keep moving it up slowly... eat a lot of fish/tuna/meat... build up so you can get at least 2700 a day!
lift at least every other day/diff body parts each day, pick three parts of the body/per day... ex: chest/tricep/legs... then next day: forearm bicep calves... etc... slowly develop the habit of lifting, then lift 5 days of the week with rest inbetween.