You are having poly cystic ovaries which means that you are having a hormonal
imbalance due to excessive weight gain
. This leads to irregular ovulation and so irregular periods
As your doctor has rightly suggested you need to reduce weight by diet and proper exercise.
As you didn't had periods for 3 months now, I would suggest you to consult your doctor.
If you are sexually active, need to rule out pregnancy
Your doctor will give you medication for withdrawal bleeding.
Also, need to check hormonal profile like thyroid
to rule out any other cause, if not checked recently.
Hope this information is helpful to you.
Dr. Mrs. Sumeet Baheti