Too much junk food still skinny?

so for that past 2 months ive been buying junk food and hiding them, id eat about 2 bag of chips everyday and some ice cream and all that, not skipping breakfast lunch or dinner. im doing this on purpose so i can gain some weight... i am currently 5'8 and weight 144 lbs(underweight) according to BMI. and im a male. and i still weigh the same... ive been conuting calories as well, to much about 4k a day! should i try weight gainers protein shake? any tips on to gain weight...? or am i already fat enough, when i look in the mirror i feel fat but when i get on the scale im so light. and everyone tells me im skinny, err iono life is confusing