Milk Drop

When my little fellow turned 3 months (October 2nd), I was overjoyed at the thought of getting to pump every 4 hours instead of 3. But now that I have, I can tell a significant drop in my milk supply. Where I would usually pump a minimum of 6 ounces, now I barely do 3. If I have to go back to pumping every 3 hours I might have a breakdown, but I'm scared to death my milk is drying up. My boobs never feel full when I'm pumping or getting ready to pump anymore. Before I would sometimes have to pump every 2.5 hours just to keep them from getting engorged. My bare minimum goal was 6 months. I don't even have enough milk to freeze at the end of the day anymore. What have y'alls experiences looked like the older your baby gets? Does this happen usually? First baby, and no one in my family breastfed so I don't really have anyone to ask.