Don't stress too much you could be like my SIL - once the m/s kicked in she lost 8 kgs so now at I think 31weeks she is only 2 kgs heavier than she was at the start. I'm 12 weeks and also overweight and I am slightly under my starting weight as I have been eating smaller meals and have been a little off my food even though I don't have m/s. You need to do light exercise like walking and don't eat for two and you should be OK. I think that's a mistake a lot of ladies make - eating way too much - but all the books say you don't need many more calories whilst pregnant. Also the healthier you eat then the less chance there is of you putting on excess weight. Good luck.