How do I keep getting fleas? I had no pets, no dogs, no cats, gerbils. Yet every other morning I need to spray my bathtub to kill fleas.?

Then if they are fleas you are likely to have 'pets' in your home you are unaware of like rats/mice

This has happened to me a few times before. You can look up life cycle of fleas, they are hard to get rid of and will keep coming back until you get it done properly. The eggs can live in carpets, furniture, etc. for years, so if you recently moved in (a few months) or brought home furniture they could have hatched. We got a new futon once and they came in via the mattress. Or if you have outdoor furniture, they could get on there via local animals (cats, squirrels, etc) and then when you sit on there you bring them in the house. They will feed on humans if there are no animals and continue breeding, making out worse and worse until you kill them all. You can get the chemical sprays at a place like Home Dept, make sure to get the ones that continue working for months. Once it was so bad we had to get an exterminator to treat the house. Good luck!

How are there fleas in your bathtub unless they're coming out of your hair?

your whole house needs to be bombed. They are very persistant.

Once you have an infestation of fleas they hang around, regardless of whether you have any livestock. You need to do something to get rid of all the fleas, not just the ones you find in the bath.