break-through bleeding again or...?

I've been on my birth control for about 10 months now. Last month (Feb 2012) I was home unexpectedly from school and missed the first few days of my new birth control pack because it was at school, so I didn't take it. My boyfriend and I had sex a couple times but then stopped because we don't use condoms and he uses the "pull out method" (I know that isn't an effective way to prevent pregnancy). I started taking my birth control on Feb 28, so I'm about three weeks in. I started to have a little spotting yesterday, but I shouldn't have my period for another 5-7 days. I wasn't sure if I would have break-through bleeding again or if it could be implantation bleeding. I was also home two weeks ago, around when I restarted my birth control for this month, and we had sex a couple times and I was home again this weekend, and we had sex again a few times. I took a pregnancy test last night, and it came out negative, but I'm not sure if it would be to early to tell? Since I'm a little more than five days before when I'm supposed to have my period.