J.C.
I would say it is a combo of it being a stage and the less sleep he seems to be getting. I wouldn't stress. If you want to make the milk easier for him to adjust to, start by mixing it 3/4ths breast milk to 1/4 milk, and over time slowly increase the ratio until it is all milk. That is what worked well for my boys (only we used formula since that was what my boys were used to).