Unprotected sex march 31rst, morning after pill 10 hrs late. april 6th five days later positive pregnancy test. was she already pregnant?

Maybe: It is possible that fertilization occurred prior to taking the morning after pill. That pill will prevent 7 out of 8 conceptions, so it's not perfect. It's also possible that a pregnancy test could be positive a week after conception, they are becoming very accurate. However, it's also possible that she conceived before 3/31. Unfortunately it will be very difficult to determine that.

Need Ultrasound: Yes. Most likely. But you need a dating ultrasound to see when you conceived.