It's normal for babies to nurse a lot and fall asleep at the breast. If your baby is only 4 weeks old I wouldn't limit sucking either. You are still establishing your milk supply and he is still vulnerable to nipple confusion. A baby suckles differently on a bottle or pacifier than at the breast and can have difficulty switching back and forth. I would just tell yourself that you are going to be the human pacifier for the next few weeks and make peace with it. It'll pay off.
Feeling like you have a baby attached all the time is normal. Keep in mind that he's growing and will eat more during growth spurts (you are probably in one now or just past it). Babies eat 8-12 times a day, and that doesn't mean every 2-4 hours like clockwork, it means if they sleep for 4 hours, they "missed" a feeding and will make up for it elsewhere. My son has been a super nurser and has always nursed a lot.
If you are really feeling run down by it, I'd suggest getting a sling or a wrap that you can wear your baby in, and if possible, learn how to nurse in. Then you can move around still. I make and sell them for $30 - a Moby style wrap and a Maya style sling. You can look at www.onebighappy.net, or try going to Peapods in St. Paul or looking into a NINO meeting for options to try them out. I couldn't get along without mine, and I've only got one 16 mo babe!
I would also suggest attending a La Leche League meeting if you're frustrated. I am part of the Plymouth/Wayzata group and we meet tomorrow night at the West Health building off 494 and 55, or check them out on the web.
Good luck!