it might sound weird but if you are active and being very cautious about what you eat, you might not be eating enough and putting your body in a constant starvation mode. meaning any fat you do intake gets stored right away.
i have seen this happen first hand. loosing the first 20-30 lbs worked great on little food and high exercice. but there was always a wall where no more weight would come off no mater what. since eating alot more food now the weight is coming off, another 20-30 lbs passed the wall which is unheard off in this case.
the initial phase of this 'diet' does put on quite a few lbs, but thats normal, then it will continue to melt off 2 lbs per weeks as long as you eat enough food.
check out a calculator such as this one and follow it carefully. its so much easier to follow a 'diet' when you are not constantly hungry.