I think if you think he's tired, he probably is.
It sounds to me like he isn't able to get himself into the next sleep cycle. Overtiredness could easily be the culprit, as barbie suggests. (I would also recommend the book Healthy Sleep Habits, Happy Child. It's hardcore cry-it-out, which isn't for everyone, but has a lot of good medical information on sleep.)
The No Cry Nap Solution (Elizabeth Pantley) offers suggestions for helping LO get into the next cycle -- the only one that worked for me was keeping the boob in the mouth, unfortunately. Her main idea is to soothe the baby (as you would when you put him down) before he fully wakes, easing him into the next cycle. This can be done using patting, his mobile, reinserting the dummy, whatever works.
If he sleeps well in the pram, you could go on some long walks and get him to have some long naps, dealing with the overtiredness first and then work on lengthening the naps.
How are you putting him down? If you're feeding to sleep (like I always did) he will wake up because the boob is gone. I used to lie next to DD and reinsert the boob till I was sure she was into the second cycle. That eventually became unsustainable and we had to break the FTS association, which was traumatic.