Well, my advice would be to test two weeks after you did the deed, which should be this week sometime, right? If you were having ovulation signs, it's definitely worth the test to make sure. About the odds, it's hard to tell; I got preggo 3 times while breastfeeding AND using BC, (not pills, but BC), so it is possible. I also know women who never use protection while they're nursing and don't get pregnant, so it's impossible to tell.
I'd definitely test two weeks after the deed; if it's negative, I would wait another week and test again. If it's still negative, then you can be pretty sure you're not preggo. Good luck!