Help!!

My average cycle for the past 3 months has been 25 days. I have a 4 day period. My period ended on July 20th. We started DTD on the 21st-25th. Then again last night 7-27. I have been using Target brand ovulation tests since the 21st. It still says no LH surge!! Glow said I should have ovulated yesterday 7-27. We are desperately TTC a little girl as we already have 2 boys and I'm so worried that I have already ovulated and the tests just aren't working right? I'm trying to stop DTD 3-4 days before ovulation for the best chances of a girl. I've taken 2 tests today as well, and still LH negative! Anyone have this issue before?