Can sex make your period start early?

I'm currently on combination birth control for 9 months. Me and my boyfriend went through a bit of a dry spell for about 3 months. This month we've had sex 3 times, the most current being this past Sunday. I started to get spotting on Tuesday and now it's Tuesday night and I'm getting more blood as if my period (withdrawal bleed) is starting. I still have 3 active pills left in my pack and I normally don't get my period until next Monday. Could sex cause my withdrawal bleed to come early?