Oh dear. Sounds like a not-fun time for all. Has your son been working on any new developmental milestones? Often when a baby is practicing something new or has something new about to "click" in his brain, the sleep patterns go all wonky. When my son was learning to walk he slept something like 2 hours a night for a few nights there. I was ready to consider checking myself into an insane asylum. ;)
If no new milestones are being worked on, is he going through a growth spurt? Did he get enough to eat during the day? Enough active play? Exposure to at least one hour of sun light per day can help with sleep. (NOT direct sunlight!)
Have there been any changes to his routine lately? Visits from the grandparents, perhaps? Sometimes that can throw the cycle off as well.
If you're still breastfeeding- did you eat anything unusual? Caffeine? Chocolate? Something with a lot of B vitamins? I'm breastfeeding my son and have to take a B12 supplement. If I take it too late in the day he won't sleep at all at night. So I've been waking myself up at 4AM to take the supplement. :p
Also, pay attention to what you feed him and when across the day. Keep B-vitamin heavy foods for earlier in the day. (Yogurt, Kefir, liver, etc.) and if you give him a multivitamin, make sure it's very early in the morning.
Oh, and I forgot- try adjusting the temperature in his room. My son sleeps best if his room is *cold*. It freaks me out, but then I realize that he's the little kid that sweats like a pig if I cover him with a light blanket sometimes.