I had sex one week ago. I have a 28 days menstrual cycle. Though some times my period occurs 2-3days earlier or later than the expected date. Last month my period started on 3rd june. And my expected next period starting day was on 1st july. But, it arrived today, 4rth july in the afternoon. It was bloodish red in colour as it usually remains on the starting. I'm also having period like cramps as I get in every period. But, I have not got heavy flow yet till now (9.00pm). Is it implantation bleeding or i'm on my period?