I'm not sure about limits on weight gain. But it seems pretty obvious to me that if you have been sick then you won't have gained weight. I only gained a total of 8 kg with my DS and my OB didn't say there was any issue. He was perfectly fine, born at 42 weeks and weighed 6lb11. I was actually back to me pre-preg weight before I left hospital! I don't starve myself, I eat healthily, with lots of fruit, try not to eat too much fatty stuff, it's just the way I'm made. Try not to worry, as long as you are eating well and having regular healthy meals including all the food groups I feel you are doing just fine!