Assuming that you don't suspect food allergies (they can really disrupt sleep and make eating uncomfortable) it's possible that you have oversupply/overactive letdown. I've had this with all three kids and it down make peaceful nursing more challenging. My letdown is so strong that it's like trying to drink from a firehose, and the little ones sputter, choke, pull off the breast etc while the milk sprays everywhere! Also, the oversupply means that I have an overabundance of the thin, watery, high-sugar foremilk. It's easy for a baby to fill up on this before getting to the fat-rich hindmilk. When this happens it can cause cramping, gas, green stools and general discomfort. The foremilk also gets processed faster and baby is hungrier sooner.
If any of this sounds familiar, I would suggest searching for "oversupply" on Kellymom.com or contacting your local LaLeche League leader for tips on how to manage the oversupply. Once you learn what works everyone can be more comfortable--it's so much easier than wrestling through until they're old enough to handle the stream!
If not I would just say that in my experience, your sleep woes are not too unusual, and you're doing a good job managing them. With my son I had to bounce him on an exercise ball for AGES to get him to sleep--sometimes upwards of two hours, in fact, in a dark room. They're cheap--about 12 bucks at WalMart--and might be an easier solution than step aerobics if he needs the movement.
Alternatively, if you haven't tried swaddling, I would strongly suggest trying it. It was a must for my babies for the first several months! It helps to calm frantic little hands and arms that they can't control and is very soothing. It might be just the thing to calm your little one for nursing and to help him sleep, too!
45 minutes is a typical single sleep cycle for a baby. At some point they do learn to resettle during light sleep stage and will begin to add an extra cycle for a total of 90 minutes. My youngest daughter is 7 mos and is just now beginning to have some 90 minute naps, although most are still 45 minutes.
Hang in there, K.! You're doing the right things it can just be tricky to figure out what a baby needs. I've had a couple of very challenging babies and have had to learn a lot of tricks!