Help please !!!!

Okay so my son was up all night last night till about 7am this morning & has been sleep ever since. Has only woken up to eat & when I change him of course. I've tried to keep him up throughout the day today but he will not stay up !!!!! I'm afraid he is going to be up all night again tonight. I'm thinking he has his days & nights mixed up. Anybody know how to break this ??? Please help !