Thank you all for your replies. I tried the idea about turning the pointy end of the seat (I don't know how to slide it over) and tested it on a shorter ride; it did seem to help. I didn't feel like I spent the entire trip scootching back and I didn't get home feeling like I had a big sore spot on my left inner thigh. My foot still went to sleep, though and I'm still nervous about going farther.

I'm a big fan of pilates, and it makes sense to me that doing core work would help with biking. After riding today, I noticed I started my ride a lot more recruited than when I finished. It could be that this hits at six miles is that that's about how long it takes before my core starts getting fatigued. (I recently had to stop going to the studio where I had been working out because of scheduling conflicts and haven't been faithful about maintaining on my own. I did a mat workout on my own last night for the first time since quitting, and was astounded a half hour later when I caught a glimpse of myself in a mirror, how dramatic the change in the way I was carrying myself was just from that one workout. I hadn't even noticed the encroaching tension and slouching.)

My seat does have feminine cutouts. If anything, I feel like the seat is too low. I know I'm supposed to keep some bend in my knee, and both the guy who helped fit my bike the other day and the guy who first looked over the bike when I bought it said I should keep it where it is, a bit lower than feels natural to me. Still, if it were about my own taste, I'd like just a little more extension in the down position. And I haven't seriously considered shoes yet. I've been using a pair of cross training sneakers. Could the right shoes make a difference?