Heavy clotted period then spotted over 2.5 weeks leading up to next bleed, but no bleed occurred, just more spots, then stopped. what could this be?

One possibility is: ...that you might not have ovulated with your recent cycles. Ovulation triggers production of progesterone. A couple of days after progesterone levels drop, normal menstruation begins. If you don't ovulate, you won't make progesterone. If you don't make progesterone, you won't have normal periods. The result is what we call "dysfunctional bleeding." Please see your gyro about this.