It is very rare to get pregnant during menstruation. In the standard 28 day cycle ovulation occurs about cycle day 14 and sperm can last inside for no more than 5 days.
Ejaculation outside with no penetration before or after will also not result in pregnancy. If semen gets between the lips, there would be more concern.
Hey what's the condition now...? M in the same situation and it's freaking me out too