Hi,
Welcome to ehealthforum,
The symptoms that you describe could be due to infection, hormonal derangements, ovarian problems, endometritis, PID, etc. Having occasional clots in menstrual bleeding is considered to be normal. However, if it is persistent, then further investigations need to be done. The exact cause cannot be determined without going ahead with examining you thoroughly and looking at further investigation results (especially vaginal swab/smear test, ultrasound scan, pregnancy test, complete hormonal analysis, etc). Consider visiting your gynecologist/obstetrician at the earliest for examination and further evaluation. Treatment as appropriate (based on examination and investigation results) would be started to help you. Drink plenty of water. Take adequate rest. Maintain healthy diet.
Take care.