Stupid question

If I have irregular periods how would I know when to take a test? I googled it and it says you can start testing 10 days after having sex but I have no clue if or when I ovulated and am not sure when I’m supposed to get my next period it could be tomorrow or three weeks from now I have no clue 🤷🏻‍♀️ so when should I start testing? Ten days from the last time ? TIA