Open Question: im 21 and i had like a terrible itch?

in my head and felt something and it was a bug and then i found like 3 lice they were like a dark color it wasnt white anyways how the heck did i get them I wash my hair usually everyday sometimes like maybe at the most I won't like 4x out of the month!! I have a son but he's not in day care and I checked him he don't have any where do these things come from and how did I end up with them its so gross!!!