Implantation bleeding or period?

Most pregnancy tests should be taken on the day of your missed period, and not before because it could cause a false negative (the test says you're not pregnant and you actually are, but took the test too soon). I believe most blood tests done at the doctor's office can detect the pregnancy hormone before your missed period. This same situation happened to me (only I wasn't on birth control) and it turned out I was pregnant, but of course, no woman's body is exactly like another one's, so I'd make an appointment to see your doctor asap to take the worry off your mind. Get a blood test and see what's up. Or, even better, go run down to the drug store and get EPT or First Response (I recommend getting the 2 or 3 pack, not just one test) and take that test right now. If it's negative, go to the doctor anyway. Good luck.