Although it does sound quite strange, this is a very common complaint for patients, so you are not alone. The sensation you are feeling is not actually diarrhea and constipation at the same time, but your symptoms explainable. A very common condition that is consistent with your story is Irritable Bowel Syndrome
(IBS). IBS patients typically complain of abdominal pain
followed by diarrhea and a feeling of incomplete evacuation (tenesmus). The abdominal pain goes away, but the feeling of needing to go continues. These symptoms will change from week to week with intermittent diarrhea and then constipation. The syndrome is more chronic than just a few days, so your symptoms may just be due to gastrointestinal virus. You will have to see how quickly you get relief. Very severe constipation can also cause loose stools. If stools are hard and are not moving, they cause back up of more watery contents behind them. Eventually the watery contents spill around the sides of the hard constipated stool and cause sudden diarrhea. This is another instance when constipation and diarrhea can seem to appear together. I suggest you keep a bowel diary describing your bowel movements (type and number) each day and schedule an appointment with your primary care physician
. He or she will take a more detailed history and perform a physical exam which will provide you with more answers. Good luck.