Spotting for weeks. Pregnant or messed up cycle?

Looking for feedback.  I have always had a regular period.  This month I got it as expected for about 3 days.  Then stopped for 1 day.  Then started over again (cramping, light to heavier) for 3 days. Ever since been lightly spotting (2 weeks).  pregnancy tests negative.  Doctor said to give it another week and take another test Or possibly just irregular.  Anyone else ever experience? If not pregnant, will it throw off my cycle dates??