I agree with Lulu, I think he may be having too much wake time for his age. A bub his age can usually only handle between 45 - 60 minutes of wake time (including a feed). When they get overtired they actually fight sleep and are unable to nap for long periods. Watch for his tired signs (jerky movements, grizzling, eye or ear rubbing, etc) then put him straight to bed.

Re: feeding. Every hour does seem like a lot, I was feeding my DS two hourly at one stage because he just wouldn't sleep properly and he ended up with reflux and was very unsettled. I started stretching out his feeds to 3 hourly and he was better within a few days. You may want to try and stretch from 2.5 - 3 hourly, but it is totally up to you. It may not be a problem for you at all, but I'm just making a suggestion.

One other thing you could try if you are really desperate is a baby hammock. My eldest DS would only sleep in my arms during the day too. After a trip to a paediatric chiropractor we discovered his right shoulder was dislocated from birth (this wasn't picked up until he was 10 weeks old!) he was much better, but still wouldn't sleep in his cot. We bought a second hand baby hammock and he LOVED it! He loved the motion of the hammock and the feeling of being snug (just like my arms would have felt to him). It was our life saver. I could resettle him easily by giving the hammock a bounce and he ended up becoming a great sleeper. You can hire them if you ever want to try them out.

I hope you find something that works for your DS soon