How to get rid of fleas with no carpet or pets in house?

Why do we have fleas? We have no pets in the house our outside dog has been bathed and doesn't have fleas and I treated the yard. It started about a month ago since then I have vacuumed EVERY day and mopped at least 2 times a week. I have since thrown out the only area rug we had in the house(the rest of the flooring is tile) I have treated all the furniture and upholstery, and washed all bedding and clothing several times. I am SO frustrated and don't know what to do. Does anyone have advice on how to get rid of this with out a flea bomb i have a 1 yr old and it's just not something i want to do.