1st Round Clomid No AF but BFN

38...TTC #1...one MC. Started first round of Clomid last month. AF due on 31st had the worst symptoms cramping, sensitive nipples, indigestion (which I never have). I am never late normally a day or two earlier then my predicted date. Only had sex twice during fertile window so really wasn't expecting anything.  Took test and BFN. I am lost...do you think it's the Clomid? How long should I wait to contact doctor?