I am 21 years and have irregular periods for 3 months im not pregnant or taking birth control pills suggest me a medicine for irregular periods?

In addition to checking for pregnancy it is usual to check your thyroid and pituitary and possibly hormone levels. A pelvic ultrasound might also be indicated. If all of that is normal than the birth control pill will regulate your cycles most effectively. You may be able to manage this through a virtual visit in the HealthTap primary care clinic.