Right now i am having cramping as if period is coming, with brown discharge, been a few days, no period. should i be worried of something serious?

Cramping, no period: I usually tell my patients to take a pregnancy test first - could be sign of implantation, ectopic or miscarriage. If test is negative, it could mean that you ovulated later than normal. Even in someone previously regular, this can of often be part of the normal variation of the cycle. However, medications and other problems, like thyroid, can do this. See your doc if persisting. Best of luck!