Glenda is right, progesterone should be fine if you are pregnant. Many of us take prometrium through first trimester or after ovulation. False positives are uncommon, but I can tell you that the blue dye tests seem to produce them more often then the pink dye. I would see your Dr. for a blood test. I wish you luck!!
You should check with your dr. I was on Prometrium (progesterone) from 2dpo and through my 1st trimester, so that shouldn't be a problem. A neg blood test could be mistaken, IF it was done too early. Best wishes.