Opt positive after sex ?

Taylor • TTC since September of 2015 for Baby #1. I have the Mirena for 4 years and I had it removed 6 months ago.
So last month I had forgotten to take my opt first thing in the morning. When I got home from work my husband and I had sex and so after sex I checked my opt. It was positive. Could it have given me a false positive ? This month I have yet to ovulate. And was suppose to ovulate 2 days ago but all tests are negative. Opinions/comments needed. Thank you! :)