Help? When did I O?

I didn't use opk's month. DH and I were actually thinking about taking a break. I took a test last night and this morning can't quite tell if I see a line or not. Showed a few coworkers and they say yes...but then again they could just be trying to be nice or sensitive with me lol. I'm thinking I may have o'd on the 20th. Trying to figure out my DPO. I saw some girls getting positives at around 11-12 days. Do I guess what I'm trying to know is when did I o so I can mark my test. And/or do you see a line faint or not???​