Negative to positive test?? Help!

Has anyone ever repeatedly gotten a negative test, even after being a week late for period and then it turn to positive later on?

I have many symptoms, things I have never felt before and my friend who is also pregnant is convinced that I am but I am very confused. I have taken multiple tests, 3 faint positives within 2 days with different brand tests and 2 negatives the next 2 days also with different brands.

I have a distinct nauseous feeling, almost like stomach acid in the pit of my stomach. I've had light cramping in lower stomach, strange feelings behind belly button area, sore boobs, and dull lower back pain. I've also been constantly burping things up for a week now. (Indigestion?) I started spotting brown two days ago and now it has stopped. My period is around 4 days late, but if I conceived later in my cycle would it still be too early to show on a test? I do have a history of irregular cycles.

Normally I see a negative test and I don't doubt it but I've never experienced these symptoms and I feel like something is up! Is it possible I'm pregnant and it's just taking longer to show up? Has anyone else experienced negative tests even after a missed period and then found to be pregnant?

Thanks!!