As long as you're eating to hunger and thirst, it really doesn't matter your size, it may just be healthy for you. Have you ever had your thyroid levels checked though? You may have an overactive metabolism, or hyperthyroidism that may affect breastfeeding if not properly controlled. I have the opposite, hypothyroidism, and I'm on medicine daily for it. But certainly your weight or size doesn't have an affect on your breast milk I wouldn't think.