26yr old now >2wks late beta serum hcg 6days late was neg. intermittent nausea hot flashes constipation headache fatigue freq urine..?preg?other ideas

Irregular periods: Irregular periods are one of the most common problems obgyns treat. If this is one time problem it usually resolves on its own. If this is a recurring problem you should be evaluated. Infections & hormonal changes can cause. Since your pregnancy test is negative you know you are not pregnant. There are many options available to help regulate the menstrual cycle. Schedule a visit.