Am i getting fat, if so how can i get skinny again without gaining muscle?

I am 5' 4" and weigh 107 lbs, but I have these stretch marks above my knee on the lateral sides of my legs. I don't think I am fat, but have gained a little weight. I don't think it was so extensive as to create stretch marks. So, could this be because I might be growing or simply have to face the fact that I am getting fatter. =].. I'm confident, I just want to maintain consistent with myself.