Chlomid advice!

Hello!

My husband and I are trying for baby 2. After a year or trying and nothing my doctor finally put me on treatment. He gave me chlomid and his instructions were to take it on day 5 of my period. According to my glow app, my period was supposed to start on Friday. It didn’t, (not surprisingly). So my question is, should I still take the pill on what would have been my fifth day or I have to wait until I get my period to take it? I tried calling my doctor but I can’t reach him. Any advice would be great help.