Ovulation Advice Please!

Sarah • TTC since April 2016. MMC #1 Sept `16 MMC #2 Jan `17 Ectopic and Tube Removed Nov ‘17
Very new to all this (on month 4 of trying after a couple very early miscarriages a few years ago) and I'm just wondering about ovulation dates etc. So OH and I had sex (and used preseed) on the 12th and then he went away for the week, I took an ovulation test and it was positive/high on the 15th and my BBT spiked. Is there any chance this could have worked? Or is there no real chance I could be pregnant with ovulating 3 days after sex? Sorry for the long post, I'm just driving myself crazy over here 😥 please help.xxx