A.L.
I have a 13 month old little boy, and when he did that very same thing it was because he was teething. He began teething off and on from 3 months until he finally got his 2 bottom teeth at 9 months. I would try orajel, tylenol, or motrin and see how he responds. If it continues, it could also be an ear infection. Have that checked out. If all physiological causes are ruled out, then I recommend the book "Baby Wise." I used it faithfully with my son, and he sleeps like a dream at night and during the day. Good Luck!