sleep regression

My son was born prematurely and I believe he has started the "sleep regression" at 5 months rather than 4. He wakes up almost every hour, sometimes every 40 minutes, all night long. He wants to be rocked or nursed until he is in a deep sleep before I can put him in the bassinet. I used to be able to put him down when he looked like he was falling asleep. I don't know what to do to get through this. His naps during the day are great, but I'm back at work and have not slept more than 40 minutes in a row in over two weeks. Suggestions....please help!!!