I started spotting every 2nd day since cd18. Period due now but just clots being shed. No blood flow as normal. I've pms symptoms and no usual strong?

Common problem. 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, polyps, fibroids and hormonal changes can cause spotting. If concerned for pregnancy then do a home test . There are many options available to help regulate the menstrual cycle. Schedule a visit.