Help! Does anyone know of any law or anything in California or US that states pregnant women shouldn't work alone?

I work retail/production alone at night in a downtown area, often homeless men on drugs/drunk come into my store and harass me. There is no security or other open shops in the area besides a drive through fast food place, I can call the cops if need be but I don't feel safe as a 6 month pregnant woman. Sometimes customers don't come in for hours! What if I go into labor or I pass out? Could be lying there on the floor until my replacement comes...

I can't quit my job or get another shift as my husband is a disabled vet and can't currently work, and is in school during the day. Can't afford to send our toddler to daycare. My manager (whom I see once a month or less) is clueless about pregnancy and is not very cooperative.

Any help would be so great!