So I had knee surgery on the 12th took a pregancy test before and was negative

So I had knee surgery on the 12th took a pregancy test before and was negative. I was having hot flashes today and decided to take a test. Big fat positive! Anyone have this happen? I'm nervous about the health of baby due to surgery. on a positive note I had an iud for the past 10 years. me and my husband have been trying for the past 10 months. My friend recommended I try a Mexican tea called Damiana! I used it for 1 month . I highly recommend it!