why does my doctor wanna wait?

Wondering if anyone has experience with this. I did my second round of clomid in January. My period came naturally last month. My period is now 4 days late and no signs really. I have been having intermittent cramping for two weeks now. Friday I swear I thought I was gonna start but I didn't. I messaged my fertility doctor yesterday and asked if he could order provera, I am just so anxious to get started again. He said he wanted me to wait until Wednesday and take another pregnancy test and if that's negative to plan on coming to the office for a blood test. My question is why? If I'm pregnant shouldn't it of shown up by now??