OTG - as much as I agree with KSH and Grog in most cases, I do think that yours is a little unique. Having said that, you still have to consider carefully what you are eating the night before.

As you said, because you are a big girl you burn more calories in 30 min than I would in 1 hour. Also, I seem to remember that you have a really hard time keeping your HR down. This would suggest that you are working at a higher zone and may be using up your glycogen very quickly because you can't work at a level that allows you to burn fat as a larger proportion of your fuel.

I have two suggestions. First, start learning how to make you own smoothies. You can easily make really good ones that are gluten free. I use yogurt, which I think you can have and you can substitute soy or rice milk for regular milk. These work really well for me. If I only drink 8 to 10 ounces, it holds off the wolves (I'm hungry all the time) and I can still run pretty hard without my stomach getting upset. Becuase it's pretty much liquid, your body should be able to digest it quickly, but ideally you would have one 30 to 45 min before running.

Second. As hard as this is for me to tell you right now, slow down or go back to a run walk interval so your body can use more fat as fuel and your glycogen stores won't be depleted so quickly. I know you have only just gotten to the point where you can run 3 miles in a row, but maybe you should save that for your one hard run per week right now.

I would also suggest trying some different gels. I'm an accelerade girl myself.