When to test if I have irregular periods?

If I have extremely irregular periods when should I test? Mine are so irregular that there’s no way to track when I will start my period or when I ovulate. It’s different every month, but I never miss a period. I didn’t have a period last month, and still haven’t started. I had sex a few times last month, but again, I have no clue when I ovulate.... I’ve taken a test recently, but negative of course. Anyone else have this problem?