How can I find out if I have a case for discrimination against my employer?

My employer has mistreated several co-workers over health issues including myself. All of us are women. Three of the five men who work in our department all have full-time Monday through Friday daytime hours and are allowed to come to work an hour later than everyone else. All other employees, women and one young man, must work a varied schedule including weekends. My employer has made condescending remarks to me and treats me like he would a teenage girl. I am 28 and older than him. He refuses to fire a co-worker who screams and tells at other employees. He threatened me with losing my job if I asked for time off due to health reasons and now claims he did not do so and that if I need time off it will be fine, but unpaid. I'm wondering if there is a case for discrimination.