Weird spotting worried.?

normally my term started like clockwork everymonth...the 28th. but later month it started on the 16th and only go to the 21st... then this after lunchtime i went into the bathroom and in that was this odd spotting...not as dark as majority period blood but ligher and and similar to a watered down red...
so i put a pad on over the subsequent couple hours i started to dicharge only brown... but not alot..
and i get the impression like a intense stomach-ache in my lower stomach not reall cramping. it's odd..
what is up, i'm not on any birth control.. You are not on birth control? Have you had sex? It could be implantation bleeding.
Well i.e. something that you should address with your doctor. If you own unprotected sex or any sexual behavior that may trigger a change contained by your normal menstrual cycle. Best item is to check with you doctor.