thank you for your query.
Asmita could be the reason for your weight gain definitely.
The reasons for your irregular periods
could be your age which is peri menopausal and resultant hormonal
other causes are endometrial hyperplasia
, endometrial polyps, cervical polyps, ovarian cysts etc.
Of course, stress, anxiety, weight gain, travelling, emotional upheavals can cause such bleeding.
other medications cross reacting could result in this picture.
Your recent thyroid, prolactin
and blood sugar levels need to be tested.
Please go for an internal check up again, and go for a reliable trans vaginal pelvic colour doppler.
In absence of positive findings on both, you could have hormonal tests to confirm peri menopause