Do you remember feeling tons of baby kicks when you were pregnant? Well, when you walked around and dd stuff, baby was rocking and rolling around inside you and sleeping away. When you sat or laid down, baby would soon wake up and start to move around. Guess what? At night, you weren't moving much so baby was awake. Baby's routine is to be awake at night and asleep during the day! That doesn't change magically just becase baby exited your uterus. It takes a while. It will most likely change within 2-3 more weeks as baby becomes more attuned to light/ dark cycles and the excitement of the day tuckers him/her out.
There's a reason they say to nap when baby naps. Don't expect to sleep at night. 2 hours in a row is all I usually get for the first year. It's normal. Babies need to eat frequently since breastmilk is digested quickly, their stomaches are tiny and they are growing like weeds!
As soon as DH gets home, I pass baby off to him and have a nap. Whenever baby is napping, I try to nap. On weekends, I have extra long naps, After a while, you will be able to figure out a better routine for getting enough sleep, and as baby grows. My DD is 11 months though and I still try to nap during the afternoon a few times a week.