In the last two weeks my bowel habits have changed from essentially normal to no stool for 2 days and on 3rd day i experience diarrhea blowouts with no pain. what could be the problem?

This sounds like natural variation in bowel function, perhaps influenced by foods eaten. But check with your doctor if irregularity continues.

If a pattern well established in spite of trying to avoid constipation, a partial obstruction is suggested. If established with a gastroenterologist that will give you the best start, if not would suggest starting with your primary care doc for an exam and detailed history, imaging tests may be needed.