Hello, I have gone through your query and understood the concern. Having a normal menstrual cycle along with pregnancy can happen only when there are uterine anomalies like a septate or a bicornuate uterus. In the normal situation, it is not possible. Since you have had several negative pregnancy tests, the cause of the delayed cycle cannot be pregnancy. It is more likely to be due to hormone imbalance. Nausea can happen also with hormone imbalance. Please also exclude urinary tract infection as you have frequency of micturition. Infections in the pelvic region and also general infections can cause delayed periods. Sudden weight changes, stress, certain medications are some other causes. Please maintain a healthy weight, healthy diet and regular exercise. A trans-vaginal/pelvic sonogram will help clarify the situation. Take care.