HSG question......

I was told you call my doctor for my appointment for my HSG test when I get my period. Its due tomorrow day 28 took a test today it was BFN. Should I call today and make it for next week? I don't want to wait till Monday and call when I get my period this weekend. I want to start my IUI and Clomid this month so I don't want to waste time. So my question is do you think it matters if I want to make my appointment because I get my period???? TIA