Early Miscarriage?

I got a bfp on August 6th late at night, the line was definitely there after 3 minutes. Up until yesterday the line was the same color for every test. Yesterday it was kinda lighter but I didn't know if I just drank too much and it wasn't concentrated enough or what. This morning I can't really see a line and I started having horrible cramps and started bleeding. I technically would be 4wks3days. It's bright red blood, but no clots or anything. Not super heavy either, but enough to have to wear a pad. I haven't even been to the doctor to confirm a pregnancy, because the lines weren't very dark and I was waiting. What should I do?