Spotting! HELP!!!

So since Sunday I've been spotting. I was supposed to start my period last week but it didn't come, I had like dark discharge. I thought no big deal maybe just old blood. But it's been like this since Sunday. But since Monday when I wipe there's blood, but when I see my pad it's just spotting. My mom said you might be pregnant some people get that. But I don't think so me and my husband have been taking our precautions. Any idea of to how this is happening? Or could it be in pregnant? Cause my mom also said all bodies and symptoms are different but I've had diarrhea since Tuesday. I don't know what to do! Help please!