Help, my milk is disappearing!

I've had overproduction from the start and even though I ended up with mastitis several times I was so grateful to have plenty of milk. But now my son is 18 months it's almost gone and I don't understand. My supply dropped like crazy. He still nurses a lot and is definitely not ready to wean, so I think it shouldn't have dropped, but it definitely has . He doesn't like food very much either so my milk is very important. He doesn't take a bottle either. I try to hand express to make some milk come out before putting him to the breast, otherwise he gets frustrated because it takes so long. My breasts feel so empty and it feels like I barely have anything in there and its stressful. His weight has also started dropping as my milk supply has dropped, and he's a tiny boy to begin with. I've eaten oatmeal for breakfast every day since he was born. I'm panicking. I was hoping we would make it until two at least. What can I do?! I don't live in the US.