False positive tests

Hello,

I am due to start my period on Tuesday and since Thursday last week have been testing and been testing positive with the line becoming much more clear as the days go on. On Saturday I did a digital and it said yes however, my doctor called to confirm the results of my bloods that were taken the day before and they are negative. I’ve done approx 10 tests and all are positive. The doctor can’t explain why they’re so obviously positive however my bloods were negative. Has anyone had this? She is redoing my bloods again in the morning.