First period after baby

Blair • Just a new mommy trying to not get pregnant again for a while :)
I am currently going on day 14 of this period and it is KILLING me! Okay so maybe not literally, but it sure feels like it. I'm on tri-linyah birth control tablet and this is also the first period I've had since having my daughter on October 28th this year. My pre-pregnancy periods lasted 3-6 days usually and I could always tell the day before my period ended because I would have a super light day. But so far I have yet to have a light day! There is no sign of this ending anytime soon :( 
Is this from my birth control or just because it's my first period since giving birth? Or possibly both..