Want to Gain weight. And improve health.

Hello, I want to gain weight and have a good physique. my routine is : I mostly skip my breakfast. I sleep late at nights and then wake up late to manage studies. Then I eat my lunch at around 3:30pm . Mostly two chapatis with any vegetable or pulses. I am vegetarian. I take my dinner at around 9:30 and before that I eat full plate apple. I have been drinking milk twice a day since childhood. my thyroid test came normal.  Before 6 months I got my Hb checked and it was 7.5. I remain stressed most of the times. I sometimes skip meals during my college time i.e. 8:00-5:30pm. I feel quite a weakness. I do exercises occassionally at weenkends. Due to lack of time I am not able to manage my health. My face has become slim and i got dark circles too. Theres always delay in my periods. i got hairfall. my immune is not so good. Family Doctor advised me ProteinX but i dont know how to take it & in what amount. i look forward to know proper diet and any proteins to gain weight and improve health.