Period Has Been MIA For Real

I haven't had my cycle since October. I had some light bleeding in November, but for me, this wasn't a normal period (it was just 2 days of very light bleeding, spotting really). My husband and I are trying to conceive, and I have taken countless tests, but they have all been negative (the most recent negative test I had was just 2 weeks ago). I have always had consistent cycles each month lasting about 6 days. What could be going on? No period yet negative pregnancy tests?