Can't BBT. When do I ovulate?

Okay, so I'm going to start my third round of Clomid this month. My doctor upped my dose to 100 mg. Last month, on my second round of Clomid, I got a peak ovulation test on cycle day 15. I can't do bbt because I work night shifts and my schedule is weird. So, when do I ovulate? They say to come in on day 21 of my cycle for a progesterone check, but that wouldn't be correct since I dont always ovulate on day 14. I asked about this before and some people were saying to check a week after my positive ovulation test.

So, how do you know when your ovulation day is if you can't do bbt?