Ovulation & ovulation strips I don't understand

[Kiehl]

Hello MN
I am 37 and have severe endometriosis. My husband and I have been ttc for months and are being referred to our local NHS fertility clinic.
I have regular periods and have a fertility app to know when I'm ovulating (which I know any way from having awful endometriosis)

My question is... I use ovulation strips, I've used different kinds but not one has come back with a 'positive' that I am ovulating.

I'm really down and I don't understand.
Does this mean I'm not ovulating? Even though all other signs are there?
I want to be clued up for the fertility clinic although I worry it'll be a long wait.

Thank you x

Ovulation tests picks up the LH surge, in some women it can last for just a few hours, so you’d need to be doing them every few hours if you fall into that category. Are you monitoring you basal body temperature? If you are and there is a temperature rise then it looks good that you’re ovulating. You can also get a day 21 progesterone level done, to check you’ve ovulating as well. Try not to worry too much, loads of people have this issue with the LH sticks, if you know when you’re about to ovulate, then that’s good!

Ah thanks Gardenlady543 this is all kinda new to me and I'm already slightly disheartened but that's good to know that perhaps it's tricky to pick up on through ovulation strips alone.
I was thinking of buying a proper basal thermometer to help

@Kiehl - as pp said the only way to know for sure is the day 21 progesterone blood test; but a combination of regular ovulation strip tests (2 or even 3 a day), basal temp and checking for egg white cervical mucus or cervical firmness/position can help (I had to use a combination of all 3 as the ovulation strip test line never got very dark for me (the pink colour "clear blue" smiley tests were clearer/better but more pricey).