Decrease in milk



I am a first time mom and exclusively breastfeeding. My baby is two months old. Aside from the first week when baby and mom were adjusting, it has been going well. However, in the last 24 hours my milk supply has dramatically dropped. I can not think of anything different in my diet and have been pumping the same amount of time. I also drink about a gallon of water everyday. Last night, while he was nursing, I felt very nauseous and threw up. Baby(who is a great sleeper) woke up a lot through the night and I know it is probably because he was not getting same amount he normally does with night feedings. Any tips or ideas of why this might be happening? No, I am not pregnant. I am spending the day nursing, power pumping and eating lactation cookies and oatmeal to try and get my supply back up.