I did three in five days on the east coast this year. Got accepted to two and waitlisted at the other. I had two different suits so dry cleaning wasn't a problem. I was tired at the end of the tour, but I was glad to save the money by scheduling them all together. I wasn't waitlisted at the last one, either. It was my first where I was waitlisted, so being tired didn't seem to play into it a whole lot.
Each interview is a little different, but like the poster above, I felt like I got into the "groove" by the third interview. Your answers become more eloquent (though you never want to sound rehearsed.)
You'll be fine. It may even be fun!