Spotting a week after my period on oct 12th then a late period. ultrasound on oct 20 normal negative urin test what's going on?

Dysfunctional bleed: Possible so called 'irregular period', functional due to hormonal or stress level changes. Watchful wait or birth control pills may be in consideration

Various possibilitie: without an exam, I can only give general information but, older ages are more serious possibilities; you are, indeed, not that old. Uterine and ovarian cancers RARE under age 40 http://www.nerdpocalypse.net/diseases/spotting%20between%20periods.html here are some possibilities, and general irregular periods things (stress, hormones, OCP's) most common.