H.J.
Okay, so I am going totally opposite of everyone else. My son can't be more than a week different in age than yours. Do you have a good baby sling? With my kids, I've found that, on the days when they seem to be having the sleep cycle you describe, the way to get 'em to take a long nap is to put the baby in the sling and do whatever you need to do--the baby is close to you, cuddled up nice and warm--he'll sleep happily. When the choice is obviously 20-minute naps on his own or 2-3 hours in the sling, I choose the sling! This worked with my now 19-month-old daughter to about 8 or 9 months, by which time she could usually be counted on to take good naps in bed.
Babies are hard-wired to want to be close to their mamas. The more they can have that, the better it is for them, and the easier it will be for you.