Hi, J....and congratulations! New motherhood is the hardest transition in life, I'm convinced. (There is now another human being in control of your life and he has yet to learn how to control his.)
The other responders who said to sleep when he sleeps and to take heart that this will eventually change are right on! This is the most exahausting time and if anyone is offering you help or a break and is a trustworthy adult, please let them! You deserve sleep and are a better mommy for it.
I am the proud mommy to a five and a one year old. What I did with my youngest is to take him for a short spin in the stroller during the times I wanted him awake and over the course of about 10 days, I taught him that day was day and night was night by not making it too easy for him to sleep when I didn't want him to.
I'd read in my sleep-deprived state that the brain uses sunlight as a cue to wake and sleep, so I tried it and it worked for us! He was also jaundiced and needed the light, so it was a dual purpose stroll for us. Your son is still really young and most children change on their own, though.
And I also made his nursery very dark, so that he got the idea that bright light meant awake and darkness meant sleep. Another aid I found helpful was to put a consistent sound in his nursery (a fan) to help him learn when it was time to sleep and when it was time to be active.
Best wishes,
C.
p.s. My son is now a great sleeper and a happy child. Even the experts' advice my not be right for you two, because everyone is different.