I need help ASAP!Now I know what most of you will say.

I need help ASAP!Now I know what most of you will say. Lecture me. But please, just save it. So I've been with this guy for 4 years. I am 17. I'm on birth control and have been for 2 years now. So last month, the day my period came, I had unprotected sex. I figured that I'd be fine, I did it before. It was on the first day of my period and my periods last 5-7 days. I've also been told that birth control is still in your system while you're on sugar pills. So this morning I was supposed to start my period. I get it on the same Thursday of every month and it's become regular since I started birth control. I wasn't bleeding when I woke up (like I normally do) but I waited it out, and soon after I started bleeding a little. Bright red. It's not heavy at all this month and it didn't even use up 1 tampon. There's still a little blood. I looked up a bunch of things about implantation bleeding and spotting, but that's brown or pinkish. Mine is bright red the color it always is. Now I'm not sure if it's a light period or what but I'm freaking out. I went to my local drug store to get a test and wouldn't you know it, sold out. I'm very stressed and need answers. Please.