Did you do any research on the traditions of Mary's early life? On how she may have come betrothed to Joseph (she wasn't married at the time).
Naturally, down through the ages, many have come up with how Mary conceived naturally.
Coptic tradition has Mary losing her parents at a young age. There was also a tradition that young girls (virgins) tended to some Temple duties, i.e. sewing, washing, etc. When the girls hit puberty, they were betrothed and left Temple service. (Again, tradition.)
In that time, 'Angel' meant messenger. Could a creative young priest (or Roman soldier) come up with a creative pick-up line for a naive Temple virgin?
As a young Jewish girl, she would have known to cause a great fuss if anyone had tried to rape her. The Temple was well traveled. So it wouldn't have likely been rape.
Keep in mind, neither of the above explains Joseph's dream or why he didn't set her aside once she became pregnant when the child was not his.