What could be another cause of missed period

Hi ladies! I need some advice (before going to the dr) My period cycle used to start on the 1st until about the 6th. In September I had no period at all. Twice, i Had very light blood when i wiped. Now, in October I had blood when I wiped for a few times. Not heavy and it probably lasted for 4hours or so. Almost a week later, I do a test. I read incorrectly and I kept the stick in my pee for 5 seconds. I later saw they say it needs to be there for 20 seconds. Result came back negative. Could the test be incorrect ? I am so confused. I've never missed a period, not to mention 2 months after each other. Thoughts? Please!.