light period...

So my cycles are pretty regular. 27 or 28 days, heavy flow days 1 and 2 then tapering flow for 2 or 3 more days. Only light cramping, nothing severe. This time has been WAY different.... I spotted for a week straight then stopping bleeding the day before I was supposed to start. Then the next day I was bleeding more so I figured my period was starting but it never got heavy enough to even wear a panty liner. It's been this way for 3 day now, what could cause this? Could I be pregnant?