While it is true that stress can effect the regularity of the female monthly cycle, however, the fact that your periods have been irregular for the past 3 years, alongwith your weight gain, points towards the possibility that you have an underlying hormonal disturbance most likely caused by Poly Cystic Ovarian Syndrome ( PCOS). The hallmarks of PCOS are hormonal imbalance, having irregular periods, weight gain, acne of the face, excessive facial hair and hair on chest, abdomen, and the presence of cysts on the ovaries. This is a rather common condition and may effect upto approximately 10% of women of child bearing age.

Proper diagnosis with the help of an ultrasound as well as labwork including FSH levels, LH levels, and serum Testosterone levels ( a male hormone that gets elevated in women with PCOS) is essential.

The second possibility is that your thyroid gland is not functioning properly, which will also cause weight gain, and irregular menses, but not acne or facial hairs etc. Tests include TSH levels, T3 levels and T4 levels.

My suggestion for you is that you should go to a doctor and get yourself examined and undergo the labs that I mentioned, as well as an ultrasound examination. I would also suggest one more blood test, and that is Serum Prolactin levels.

Between these tests lies the answer to your problem.

Good luck!