D.,
This EXACT thing happened with my daughter at about that age. I was fairly pregnant at the time and determined to not have 2 in diapers! I tried and tried and tried to sit her on the potty for 15 minutes and nothing. Then pee on the floor or whatever she was wearing. I actually gave up for a while. Jump to about 7 months later, my baby was about a month old, the older one 27 months. Her grandmother keeps her a couple days a week and just started putting panties on her all day. YES-she went on the floor, there was cleaning up to do, but she knew she was wet. Within 2 days she was asking to and going in the potty!! I personally thought it was a miracle, but it turns out she just didn't like the wet feeling and wasn't getting it with the diapers and pull-ups so it didn't matter while she was wearing them.
Try it...it might just work. :)Good luck!
PS. I also posted a response to another mama who's child had been doing well and then started wetting the bed. You might check that out too.
C.