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It is not uncommon to find women getting pregnant while being on hormonal contraceptives. Your symptoms (abdominal cramps, heavy bleeding, clots & tissue in bleeding, extreme fatigue, nausea) could be suggestive of possibility of pregnancy and probable ongoing miscarriage. If you suspect to be pregnant, consider visiting your doctor/gynecologist for further examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). An ultrasound scan done will help to confirm if uterus is empty or with retained products of conception. Take adequate rest. Drink plenty of water. Maintain healthy diet. If pregnancy gets ruled out, get further evaluation done to rule out hormonal imbalances, contraceptive related problems (due to prolonged use), endometrial hyperplasia etc as causes for the prolonged and heavy bleeding. Go ahead with evaluation done for current status of endometriosis. If found to be flared up, laparoscopy should be considered to remove the growths and get started on regression therapy for control of endometriosis.
Take care.