Hello,
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If you have been regular and strict with your birth control, then there is no need to worry about pregnancy (since you also use back up method-condoms for protection).
The stomach cramps and the abnormal bleeding could signal other problems related to your ovaries or uterus and should be further investigated.
Report to your doctor/gynecologist for a thorough examination, hormonal analysis and a pelvic scan to look for the cause for your symptoms.
Take care.