Irregular period

I will start by saying my periods are regular 99% of the time. Occasionally i will have one the is a few day late or a few days early. However I have never had this happen before. My period was supposed to start on Aug 21 and it did not. After 8 days of being late i started spotting on Aug 27. I spotted for 7 days. On Sept 4 my period started but was much light than my normal period. My period ended on Sept 10, and on Sept 11 and 12th i was spotting again. Any idea what could be going on? I have take a pregnancy test every day since Aug27 and they were all negative. I have never had anything like this happen before and my dr says there is no medical need for me to be seen.