can undereating cause mental disorders?

Well since october of 2013 up until now i hae managed to lose 30 pounds i have gone from 150 to 120. However i was kind of undereating and everything was fine until I started hving these crazy feelings of suicide and agitation and couldnt stand to look t nything. It made me go to the doctor and I told my doctor tht Im hving these restless feelings and depression and he told me to stop my ''diet'' and ordered a blood test. Also my periods hve stoppe for the past three months . Just about a week ago Instarted eating regulary no diet but I still get these restless agitated feelings and I feel like crying but cant cry and I feel hopeless and think to myself that there is no point in life No Point at all its like major depression. However when I eat without any control i feel slightly better after. Like in the afternoon I was crying like crazy and almost on the verge of committing suicide but when indrank coffee nd had a big sandwich with mayo I started feeling slightly better. I do kind of feel.restless but its ok now.I have been depressed before but it wasnt bad like this. I was just wondering tongive it couple of weeks and just eat without counting caories or anything and If i dont feel.better I will gonsee a psychologist.my bloodtest came out normal but hemoglobin wa kinda low can undereating really mess up your brain ? I was reallt being restricting and ate 1200.calories a day and I even topped losing weight and I want my period bck