What Is The Remedy For Irregular Periods?

hii..... i hv had irregular menses since the time they started...nd doctor had earlier prescribed me modus tablets...nd i used to have periods..now i dint hv that medicine since a long time and periods are more or less irregular.. i have had unprotected sex with my partner for over a month and m not getting periods every time i test for pregnancy its negetive... well can u tell me is there a problem with me getting pregnant and now should i again take that medicine to get menses??