Hello. Not having periods for 3 months is a serious matter. First of all, if you are sexually active, do a urine pregnancy test ASAP. Kits are available for that in every pharmacy. If the report is positive, then contact an Obstetrician & Gynecologist immediately. If it turns out to be negative, then do the following tests - blood for CBC, TSH, LH, FSH, FBS and Ultrasound of whole abdomen. It can be due to ovarian cysts or hormonal disorders including thyroid. Review with me in Practo Direct with the reports. Hope this helps.