Hi

I second what Raven has said, he may be going through his first "Wonder Week" leap which generally happens between 4-5 weeks. I went through something similar with my DD at the same time, she is generally a very placid baby but I had a couple of days of just constant screaming, not sleeping and being very clingy.

If you can grab a copy of the "Wonder Weeks" book (available through Belly Belly Store) it might help you understand what is happening.

The next development leap is around 8 weeks and then another at 12 weeks. I'm lucky we have seemed to have got through the 8 week one without too much drama, so the next one for me is 12 weeks.