Hi,
I don't have any advice on getting him to sleep but I do have some hope for you. My daughter was the same. From day one she would sleep 15 to 20 minutes at a time and then the longest she slept for the next 3 years was 3 to 5 hours max. We were terribly sleep deprived and thought it would never end. We ended up co-sleeping just because at least if she was up I was still laying down. I nursed her until she was 29 months.
Magically at 3 years old she started sleeping 11 hours straight!! Still in our bed but I'm sleeping and it's wonderful.
So I hope you don't have to wait that long but that's how it happened for us it took 3 years!!
I think my daughter just didn't want to miss anything and she was very alert and always wanting to look around and sleep was no a priority. We worried about her brain and her growth but she grew just fine and is very intelligent.
So I know it's a long ways off but there is hope. I'm sure your little guy will want to sleep one day. Hopefully sooner than ours!
She is almost 4 now and still sleeps with us but she still sleeps 10 to 11 hours every nigh.
D.