Are you on birth control?
Early pregnancy symptoms are very similar to the symptoms of an oncoming period. So that might be what you were feeling.
If your period was late, that could be the result of many things including stress and diet.
Clots in your menstrual fluid are also normal. They might sort of chunky or kind of stringy.
If you're still concerned, you could give us more information or talk to your ob-gyn. If it is possible that you had a miscarriage, you should let your ob-gyn know about it anyway.