What Causes Light Spotting After Coming Off Birth Control Pills?

I stopped taking birth control pills february 12th, two weeks before my expected period i experienced on and off spotting, the spotting was very pink/red and fresh and last for only two days .. I also have been having unprotected sex since, at least twice a day because i'm trying to conceive. At first i was very scared when i started to spot, but i was told it could be implantation bleeding meaning i may have conceived but then i was told it was probably a nasty side effect from stopping my birth control pills and i'm sure they're are many other things it could be .. but i was wondering if there is anyone who could give me some advice or suggestions as to what may be the problem i'm having and what to do ..