Just started a couple weeks ago myself - I share your pain.
I've had four classes so far, the last two I didn't feel quite as worn out and had an easier time concentrating. Still getting my ass kicked of course. No weight issues but Christ am I out of shape.
I don't have much of a background in anything other than about 15 months of Judo at a very young age. Anyway I love it, just wish I didn't wait until I was 30 to leave the beer at the store a little more often and get off my ass...better late than never!