I recall things settling down around three months (he was born a little bigger than yours is now, so size has nothing to do with frequency of nursing, IMHO). Around then, my son would actually let me put him down in a play gym thing my mom had given us or would watch his mobile (the only time he would spend in his crib) and let me go brush my teeth or put some makeup on The feedings spread out too from every hour on the hour 24 hours a day to something more reasonable. Like I said on the other thread, if we considered the first three months of life the last three months of gestation, it would put things in a different perspective. It goes, just as pregnancy does, and before we know it, those little babies don't really need us anymore!
Hang in there. It does get better. Getting out of the house to the gym is a great idea. I also found that I could take the baby by myself to the mall or something -- even just a store -- and just walk around during the day if I really felt like the walls were closing in.
I hated the Bjorn. Hurt my back. A sling was a much better option for us. So I'd second looking into one.