Can a miscarriage cause a positive result on a pregnancy test? My roommate had her period on March 9, and had unprotected sex after it was over. 12 hours after she had unprotected sex she took the plan B pill . Then that sunday March 18 she started her period again. Then she had unprotected sex again on april 7, and took another plan B on the 8th. When she didn t start her period on the 9th or the 18th of April she took a home pregnancy test on the 16th of April and it came back negative. Then she took another one this past Monday and it came back positive. We went to a clinic here in town and they did a pregnancy test and it came back positive as well. Then she went to another clinic down in one of the closer big cities and they did one and it came back positive as well. They did an ultra sound and they said that they couldn t see anything. The first clinic that we went to told her they estimated that she was about 5 weeks pregnant . The second clinic that she went to told her that she could be having an atopical pregnancy or it could be too early to see anything on the ultra sound. My questions to you are, can a miscarriage cause her to be getting false positives, can the plan B cause her to get a false positive, or is it really just too early to tell?