I have gone through your query and understood the concern. If you have been regularly using the pill for the past two months now, you should have a protected cycle. So, chances of failure are less. Though you have been having unprotected intercourse
even before the start of the pill, if you had the normal withdrawal bleed in every cycle, the risk is negligible. Your symptoms are suggestive of a hormone imbalance
and hence, a breakthrough bleed. Home pregnancy
tests may not read well now and you can get benefit from the blood test
for pregnancy. This can be aided by a trans-vaginal sonogram to know the status of the pelvic organs. Further management can be planned accordingly. Hope this helps.