Hi J.,
How old is your son and how long has he had his band on? It does take time for them to get used to it. Especially if they are used to sleeping on the side that the helmet strap is on. Something you can do is get a baby wedge and prop him up so that he doesnt turn to his stomache. If your son is old enough that he turns on his own, just make sure that you have a firm mattress and very little bedding in the crib. If he's turning back and forth well and he turns to his tummy/face to sleep, he should quickly figure out on his own how to adjust his head so he can breath easy.
Which band do you use? We used a DOC band from Cranial Tech. My son took a while to get used to wearing it. He was about 6 mos old when he got banded. His head sweat like crazy for a while, but he did adjust and the sweating let up.
There is a plagiocephaly site on Yahoogroups.com. http://health.groups.yahoo.com/group/Plagiocephaly/?yguid...
And also cappskids.org
Both sites were wonderful resources for plagiocephaly and banding information.