progesterone question!

Kristin
I had a miscarriage in December and my progesterone was low. My cycle was all messed up for months after...
Last month my doctor put me on progesterone for cycle days 18-30. Then I stop on day 30 and my period is suppose to come. 
Last cycle I started spotting on cycle day 24 so I knew I wasn't pregnant and it continued to get heavier each day. 
This time I finished cycle day 30 and have had no spotting or bleeding. I took a test and it was negative. I called the nurse and she said do not continue progesterone and take another test in 48 hours. But, if I am pregnant I don't want to stop taking the progesterone, right? Does anyone see my thinking here?! Help!