Hi C.!
Boy - aren't 4 month old's fun sometimes? NOT! My youngest is 4.5 months old, and I am dealing with the same thing. I am on another parenting-type board, and they refer to this as "the wakeful 4 month old". Both of my boys have gone through this at this age. Honestly, I think that they have just figured out that it's more fun to be awake and be around where the action is. But the thing is that their little bodies can't take all the excitement. I also think that it could be due to teething ... not that they are necessarily in pain, just that it's something new that they are feeling and it's keeping them awake. Growth spurt? Probably that too. See, they have sooooooo much going on right now no wonder they can't settle! One thing that I can say though is that it will pass - trust me. It seems to last forever because you just got to the point where you thought the 4 month old would sleep through the night and all of a sudden (like mine last night) they are up twice a night to eat again! Makes me want to pull my hair out! It doesn't last forever. Try to enjoy it if you possibly can though because soon they won't be babies anymore...they'll be toddlers...then going to school, etc.