Go out with someone the opposite gender
It is perfectly normal
Tell her that you are fine with her sexuality, but you are straight and find it a little bit awkward
Slowly but confidently tell her you like her and ask her if she feels the same way. Either that or play Truth or Dare and if it's truth ask her, if it's dare, dare her to tell you the truth
Either ask her or give her hints that you aren't too sure
Treat her like a friend but give her subtle hints. If she does the same, then take it a little bit further, but don't go too fast or else you'll sound desperate.
If you remember having intercourse several days or weeks after you last period, then you might be pregnant, otherwise it could just be your cycle is irregular and is trying to adjust