J.G.
Are you sure you're not describing my son? He's almost 5 years old and he is an amazing sleeper ... now! He sure wasn't as a baby!
I would mention it to your pediatrician. Some moms have mentioned reflux and other concerns. It's always a good idea to mention things to your ped, if for no other reason that to rule them out. He's probably perfectly healthy and just doesn't need as much sleep as other babies.
He is still very young, so most likely it will be at least a couple of months before he will have a consistent sleeping pattern. For now, try to remember that the best place for baby to sleep is wherever baby will sleep! It can be the car seat, the swing the bouncy sleep, your bed. Also, babies change their sleeping habits quite often during the first few months, so again, do what works. Don't worry about nursing him to sleep or rocking him to sleep. You don't need to put him to bed drowsy but awake. Just do whatever works.
I wouldn't worry about the number or hours he's sleeping. Try not to watch the clock and just watch for signs that he's tired and respond to those. Some babies simply do not need as much sleep as other babies.
Many babies slip into patterns sometime before or around 6 months. That's great! But that wasn't my oldest son. He began napping much better around 12 months and really started doing great around 16 months. Now he sleeps 11 hours every night! My younger son was a champion sleeper from the get go. Who knows why, they are who they are.
Good luck! I know it's tough now, really I do. He'll get better. Try to relax and let him tell you when he's tired.