Hi C.,
My first reaction when I read your post was relief! I sympathise 100%, and am relieved to know that it isn't just my baby behaving like this! For the past week my 4-month old, Sam, has done NOTHING BUT cry, fuss and scream. Nothing I do seems to help for more than 10-minutes, I've tried everything and I am also feeling at my wit's end.
The only thing that really makes him happy for a while is our 2-year old son, Thomas, but I can't keep asking him to entertain Sam - he has his own 2-year old stuff to do!
One thing that has worked the past couple of days is just putting him in his crib with his music playing and leaving him. He fusses for the first 10-minutes, but then seems to enjoy the 'down time'. It only works for around half an hour, but that is a God-send to me at the moment. I understand that even babies need some 'alone' time now and then.
I also remember when Thomas went through similar periods his doctor told me that sometimes when babies are going through a developmental stage they can get overly fussy and difficult. Apparently this often precedes them developing a new skill - so maybe your little one is about to start sitting, rolling, or manipulating objects, (if he hasn't already, obviously).
Hang in there C.. For what it's worth, you are not alone.
D.