milk problems

I am getting so frustrated. With my first two kids my milk dried up and went away right at 5 months. I also wasn't very consistent with nursing so I always blamed it on that. With this baby I SWORE I would figure it out and be successful. I strictly nurse her with no supplementing. It's been going great so far up until about a week ago. She is on a pretty consistent schedule of eating every 3 to 3 1/2 hours. And my milk is STILL going away. She is starting to hate nursing. Every time I feed her she fusses and pulls away. She is sucking as hard as she can and isn't getting anything out. I pumped the other day just to see if she would take a bottle since we're going out of town next week, and I only got a half ounce out of each side. That's not very much. No wonder she hates nursing. I drink about a gallon of water a day and I eat all the time, so I know I'm getting enough calories. I am so frustrated! After I attempt to feed her she is hungry again after an hour because she hardly got anything out, so I try and feed her again and she still isn't getting anything out. I feel like it's a vicious cycle, she tries to eat but only sucks for 5 minutes or so and gets frustrated and stops and so my body thinks that's all it needs to make and doesn't produce any more for the next feeding. Why is something that's suppose to be so natural and good for the baby have to be so confusing and impossible? I LOVE nursing and really wanted to figure it out this time but for some reason my body just won't do it. Any tips? I feel like I've tried everything. With Davis I tried all those silly herbs and they were just a really expensive joke. I've tried pumping after the feedings and that doesn't do anything and I frankly don't have time to sit there and pump after every feeding. Please help!!!! The myth that your body is on a supply and demand system is a joke. It's just not true. I've done everything right and it's still drying up.

I. Am. Mad. The end