It depends on which underwear you're wearing. If you only wearing your bra and had an unprotected sex. There is an 95% chance you'll get pregnant. If you mean to say you were wearing your panties on, then there no way for an actual penetration to happen. Thus no way for the sperm to swim through the cloth protecting your vagina.
underwears
Rainbow :D
No!
Grey very very grey
No
yes!!
no you perv
no obviously not
no
goodwill cause the sell donated underwears!
no
ask a parent :)