Help period??

So my period came 4 to 5 days earlier then what it was surposed too it usually come on time regularly. It's not like my usually period either and i usually have it heavy but this time it wasnt heavy at all and been more of spotting. We are trying to get pregnant for the last 3 months and started taking pre natal vitamins and was wondering if that's why it wasnt heavy and more spotting? Any ideas??