Negative blood test

I just had my blood test done yesterday and called today to get the results and the doctor said my progesterone level was positive and my blood test negative and if I don't get my period to call him next week to repeat the blood test. Usually he puts me on provera bc he knows my period doesn't come regularly so it was weird this time he suggested if I don't get it to get blood test again. Has this happened to anybody and got a positive blood test after a negative?