Breast feeding struggle at 7 months

My baby boy will be 7 months on the 7th. I have been BF since day one with an abundance of milk. So much so that even with working since he was 9 wks I still have a freezer stash. We just now started feeding him Sept. Milk. Anyway, I usually pump at work, but since I'm a teacher I have been off for a week and a half now. I figured that feeding him on demand this week would increase my supply. However, I'm finding him fussing at my breast. I've tried pumping a few times and have barely gotten any milk. I usually pump 6-8 ounces per 10 min session. Now I pumped 13 min and didn't even get 1 ounce. I have been trying to drink more water, and even drank a Gatorade today and yesterday, plus some mothers milk tea. Am I drying up? Even though he's still nursing? Can this happen? I'm so sad. I'm not ready for this time to be over. I was hoping to nurse for a year. But the look on his face when he's trying to nurse and no milk is coming out is heartbreaking.  Has this happened to anyone else? So frustrating.