OPK help!

Ignore my stained hair color hands (cosmetologist). We’ve been trying for 4mo now. My cycles are 33days long. I usually ovulate CD 15-18. I have yet to get a single positive opk on any of these tests but I know I’m ovulating from other methods of tracking. This is the darkest I’ve gotten. On CD23!!! What the heck gives?! Does anyone else have awful luck with these things? Should I try a different brand or what? I feel like I’m wasting my time because they’re always off. Or am I just reading everything wrong. SOS! Help 😂