PCOS and trying to TTC

I have PCOS - and am TTC. I don't know how long my cycles are as they vary! But i got a positive ovulation result earlier in the month and according to this app and another I use it says I'm due in 3 days? When is the best time to test!? I'm currently 11 days DPO and have been seeing creamy CM on and off over the past week! I did a test 2 days ago and got BFN :(