Positive and negative tests

Hi,

I took a preg test this afternoon (clear blue digital) and it was positive. I had no reason to test other then my friend found out she’s pregnant today and I had a test so I did.

I went out and got 3 more and all were negative this afternoon.

Today is dec 1. I haven’t missed a period. And haven’t had sex since my last period (sex on Halloween). But am on the pill and we use condoms. So I don’t understand how i could be pregnant realistically...

Anyone else have a false positive then negatives? I am on water pill for another condition. And an allergy pill. Not that that means anything.

Help?!