Brown Spotting

So, I've had brown spotting for the last five days. Very light, usually in the morning and then very minimal for the rest of the day. I've had lots of cramping l, back ache and slight nausea, but those are the only symptoms, no breast tenderness. My period was due Friday, October 2nd. My periods are never this late. The last 6 months I've been right at 29-31 days. Today I'm at day 35. I broke down and took a hpt this morning and BFN...has anyone else experienced this? I'm worried. I've never missed a period in my whole life or had anything else similar to this....