I think if you definitely got a bfp at one point chemical is likely
If the test was maybe not reliable one possibility is that you have had an anovulatory cycle, if you did it would explain why your next cycle is not usual either- chances would be you ovulated much later than normal for your dec cycle because your hormones were off.
- I have had these a few times confirmed by the doctor with similar symptoms. Simply failed to ovulated. I had pink tissue in clear cm, and I had two periods, about 5 days between the two. The first was light, and the second was normal but didn't last long. I also had about 8 days of period type cramps, as well as all the symptoms of pregnancy! when that happens it all comes down to hormones, it can make your cycles very odd until you ovulate again because your body has to re-balance hormones.