Hello, I have gone through your query and understood the concern. As you have been on the oral contraception for so long, hormonal imbalance should not be an issue. However, weight gain is a common occurrence when hormones are used and this can lead to hormone imbalance and irregular bleeding. Coagulation profile also should be done along with a trans-vaginal/pelvic sonogram to know the status of the pelvic organs and to exclude any cysts. Hepatic function is also important as impaired function can cause bleeding. Hope you find this information useful. Take care.