What Causes Delayed Period And Brown Vaginal Spotting While HPT Is Negative?

I was 6 days late for my period. On the 6th day at night I had a orange streak of blood when I wiped. The next day I passed a small clot with no other bleeding at all. Then I spotted a very very small of pinkish/redish blood the following day that turned brown. Then seems to stop. Took a pregnancy test and it was negative. Trying to get pregnant and I don't understand what is happening. Period is very regular 29-30 days. Please help. What else could it be if since negative pregnancy test?