having a mood problem

it feels like i have been on diet for ages.. when i look into the mirror i dont see any difference.. kinda frustating.. with that also i am starting to get cranky and i easily blast people who just make simple mistakes.. is it because i am getting malnourished? it must be the food withdrawal syndrome.. hard to explain.. i dont even feel hungry but i do feel i get sleepy easily.. i've read that when ur brain is lacking of oxygen u start to yawn.. so like i am yawning every 3 minutes.. mind boggling.. maybe i try to look it up on the internet and if i get the answer i'll post it here