Milk supply dropping suddenly

Anyone out there that can give me some advice on what I can do to get my supply back up? I was getting three ounces while pumping, about twenty minutes after feeding lo, but now I'm lucky if I get an ounce an hour later. I'm trying to increase pumping frequency to prepare to go back to work in three weeks... I'm using mother's milk tea, oatmeal, pumping, drinking plenty of water, eating greens and fruits... Suggestions please?