I've been getting my period 3 days early for the past 4 months. should i be worried? what could be the cause?

Likely normal: Unfortunately, monthly cycles are not set in stone. It is possible for your hormones to cause changes in your cycle that are not at all pathologic, but just an adjustment to a new normal. Although inconvenient, it does not necessarily indicate a problem. If concerned, a doctor can do blood testing that will ensure that your hormones are at normal levels.