Hi Heather,  Is your son a salt waster?  Somewhere along the line I have heard or read that saltwasters, if they are low on salt become very sore all over.  I have tried different things with my 27 month old salt waster.  He has always been a very calm baby.  When he is having a bad day (a lot of whining) I give him a little bit of salt straight in his hand or mouth, about an hour later he stops whining and acting up.  So maybe there is a connection between soreness in the body and the sodium levels being a little too low.  Hope this helps.