As dgil mentioned, don't worry about your weight at this time. Enjoy your training. Do conditioning on the side but when you train hard, weight will come off.
When I was training, the first thing I noticed was that I blew my gastank immediately. It was just an adrenaline dump and then I was vulnerable to my partner's onslaught. I learned to pace myself, which helped a lot. Also, it took me a while to getting used to getting hit in the face. Countering and circling out took me a long time to learn.