help?!

so I started on a birth control / hormone (Aygestin/Norethindrone) pill on the 2nd day of my cycle in November because I was having surgery on my tubes 12/1 and my doctor didn't want me bleeding or pregnant. i stopped the pill on 12/16 because my period was supposed to start the next day, which it did & lasted the normal 5-6 days.. today I started spotting and right now it's looking like I'm about to start again but my period isn't due for another 10 days! is this the effects of not using bc anymore or what? originally I was thinking implantation bleeding but now it's a little heavier? my period has NEVER been this early and is always right on time every month?!