Period???? Or what?

My period ended on Saturday and I had sex with my boyfriend this morning before I went to work and now I'm at work I just went to the bathroom and I'm bleeding. It's more than just spitting though it's like I got my pd again! Is this from the sex cause it to come back? Or does anyone have other suggestions of what it might be? Sometimes after we have sex there's a tiny bit of blood and it goes away but this is more than that it's a good bit. Can someone give me some insight?