I recently had safe oral and vaginal sex while away on business. Upon my return I had unprotected sex with my girlfriend and now she is experiencing itching and redness in and around her vagina. Could it be possible that I contracted a std or sti while away and passed it on to my girlfriend within days and if so what type of std could it be? I don't really have any symptoms besides a little itchiness on my testicles.

Here's some possibilities,

This could be a classic jock itch infection that has responded as a yeast infection to your girlfriend. Jock itch and yeast are both caused by yeast and it can come from not drying off well after a shower or sweating.

That's the good news.

Should you see any clear fluid filled blisters, then that may be a sign of herpes. Herpes can be transmitted by skin to skin contact so if a condom is not protecting the infecting skin, you can contract it this way.

Also crabs or pubic lice can cause redness and itching as well. It's best that your girl gets checked out by her doctor so they can begin a course of treatment as well as yourself. I'm hoping it's just a yeast infection thing going on or just jock itch.

BV or bacterial infections can cause itchyness as well as redness. Just FYI.