birth control but pregnancy symptoms!

Hey y'all! Just to give a few details I'm 20, and I live with my wonderful boyfriend. Kids are a terror for me(I have 2 very young sisters, they are birth control alone lol) and I really wanted to take the best measures of birth control that I could. So in late sept I went to planned parenthood and got the rod arm implant birth control. It's cool lol
Cut to this month I had my period on the 6th - 10th of February it was normal, and then on the 13th of February I got intimate with my boyfriend. Today is the 17th and for the past 2 days I've had extremely light bright red watery blood. It's even lighter right now so I think it might stop soon. And also my breasts have been a lil sore and they look HUGE ! I've also been peeing a lot despot not drinking much, I also have horrible cramps (normally I don't have cramps in my stomach only my back) . 
So my question is.... could I really be pregnant on this birthcontrol? I have never felt this way before. Please help! I need some gals who know a thing or two about vaginas lol