Suggest Treatment For Irregular Periods

Is there any over the counter drug to make me have more frequent periods? At one point i didnt start my period for 7 months, then i started for only like 2 days as i remember, then like 2 weeks into i had irregular blood, it would make me think istarted my period but it would only be for that point in time, i'd insert a unscented tampon & take it out and it would be slightly red but not all over the tampon, only on certain spots...iam sexually active. my last period i dont know when it was i just bleed on certain days and it goes away, i don't really want to go into the doctors office, i just wanted to know if there is any over the counter drug to help me start my period back up, thats cheap and guaranteed to work.