my DH is back to work today too. i'm not so much worried about the baby as the other two kids - they've been following him around for 2 weeks now, they're going to miss him so much

and of course it's raining here today, so i can't even get them outside to run around. it's going to be a long day.
Xekomaya - have you tried wearing the baby? Elowyn pretty much sleeps in some sort of carrier most of the day, it's the only way i can get anything accomplished, get the other kids fed, etc. and once she's asleep from the motion of me walking around, i can sit down and she stays asleep. maybe you could try that, and see if you can catch a catnap in a recliner or something? that whole 'sleep when the baby sleeps' thing is really important if you can swing it. DH let me and the baby sleep till 11am yesterday and i was like a new person when we woke up! it was the best mother's day present ever!
and i agree with treehugger, if you're not cosleeping you should! it makes life a whole lot easier. if you are, then just try and focus on sleeping for short bursts whenever the baby does. if baby doesn't like laying on his back next to you, try laying him tummy to tummy on your chest - babies love to hear their mama's heartbeat! sometimes white noise or music can also help a little one stay asleep. my DD1 had to have music playing while she slept when she was little or she'd wake up every 30-45 minutes all night long.
and remember, this phase really won't last forever - it just sometimes feels like it when you're in the moment. as he bulks up and his tummy grows, he'll be able to hold more milk at a nursing and will then be able to sleep for longer stretches. time seems to stand still for those first couple of months with a newborn, but it really will be no time before it just seems like a hazy memory!