You have gained a considerable amount of weight in the last two years. With this much of a weight gain I would have to say that the stretch marks are directly related to this and in fact very normal. Skin is very elastic if stretched over a length of time, however when stretched quickly, unfortunatly, stretch marks are usually the result. I would consult with your MD about the weight gain. It is possible you need to just switch the brand of birth control you are taking. Good luck to you.