Worried!

Marie
So My period ended about a week ago, and ever since it stopped, I've had spotting and just last night after having sex with my partner it seems like I've started a second period?! I went pee and at first I thought I had peed blood, but then later during the night I went pee again and kind of looked to see where the blood was coming from and it's not with my urine... It's exactly like how you bleed when you pee while on your period except it's more runny and not as thick as it usually is for me... It's not a regular amount of blood, it's a little less and lighter colored than usual, so I was thinking maybe it was implantation bleeding and I could be pregnant? I have no pain, and my breasts are tender like when I'm right about to start my regular period. But I didn't think I'd have ANY signs of pregnancy this soon, it's only been a week since my last period, and we had sex on every one of my fertile days and during my period with no protection. 
Is something wrong or could I be pregnant? I'm terrified and so is my fiancé... Please help.