Me and my fiance have been trying for a baby and now my periods a week early.. What does this mean!?

Hiya basically me and my fiance are trying for a baby and at the end of May I stopped taking the contraceptive pill Yasmin and was due to get my period on the 9th June, though it didn't come until 13th (I had only been on Yasmin for a little under two years and still continued getting my periods whilst on it but I'd heard that your body takes a while to adjust itself once you've stopped taking it) Anyway my next period should then have come 11th July but the Monday that's just gone, the 4th, I started getting a light bleeding which lasted a couple hours. Then the next evening I bled again and have continued on and off until this morning. It was not like my usual period and I don't normally get cramps, headaches or any other signs before/during my period so I've got nothing to judge it against! I have just done a pregnancy test and it came back negative but I'm so confused - why is my period a week early, am I pregnant? Please help!x