We had the same thing around the 5-6 week age with ds2, he'd go to sleep for literally 5 minutes and then wake up, this lasted for about a week and then he went back to a better sleep pattern. As others have said there is a growth and development stage around this age, and it does pass (doesn't seem like it at the time though )! I borrowed a copy of the wonder weeks from our local library, I found it really explained the 'fussy' stages which coincide with major developmental stages. Hope you have a better day tomorrow