no matter how much exercise.....

I have worked out extensively for the past month - almost everyday. For up to an hour (in 2 half hour slots - rowing machine and cross-trainer)but I just can't seem to get under 12st 10 pounds. Its incredibly frustrating especially as a) the end of the year is now only a couple of weeks away (with Christmas in between!)and b) my target weight was 30 pounds lost in a year. I'm bracing myself for failure :-(

However I have lost 22 pounds so far - so its not a complete washout :-)