The only way to know for absolute certain that you ovulated is to temp. It is possible to get all the other signs of ovulation but unless your temp rises ovulation can't be confirmed. The other observations are only secondary and temping is the most accurate and reliable.
Yup, this is really the only way to be sure. If I was charting to avoid, I'd wait until temp increase and then 24 hrs before DTD. I don't think CM is reliable at all. I've had cycles where the egg white CM came and went for days, and I kept thinking I'd ov'ed but hadn't. The cycle we conceived DD I ov'ed on about day 18 I think, and we would've totally missed the chance if I hadn't been checking temps.

If you ov'ed on day 16, which sounds possible given your usual cycle length and symptoms, yes, you could've been fertile on the day after. If you are really concerned about the possibility of pregnancy, you're still within the window for the emergency contraceptive if that is something you would consider. You have up to 72hrs after DTD.