Just a few suggestions that I can think of :-

Milk coming in/engorgement/mastitis = fever
Any placenta issues with the birth of your beautiful boy?
There are some really bad throat/flu/infections going around involving a temp
I am not sure if you had natural birth - but if you have stitches anywhere, no sign of infection or increased soreness?

Hope it is nothing and you are just a bit run down. But that high temp would indicate infection of some kind IMO.