Question about losing weight...please help?

I need to lose some weight. Since I was really young I would barely ever get hungry and definately wouldnt overeat but I would still seem to gain weight! So I went to a nutritionist and she said to start eating more to speed up my metabolism. The problem with that is when eating more (even though its healthy food) I end up gaining some weight or staying at the same weight. When I start eating less (2 meals a day or less) I stay the same as well. I'm just really confused. I also do exercise between cardio, dance cles, weight training and yoga.... so I am active as well. I'm not at a healthy weight and I'm concerned... though the doctors have found nothing medically wrong with me as far as not being able to lose weight (thyroid probs and such). Any ideas on what I can do?