Dpo and testing

Jackie • Baby boy born 10/17/16 Baby girl 09/14/18 🤰 with #3

So I got a positive opk the 16th and 17th so I’m not for sure when I ovulated. Ovia says I’m 8dpo as it says I O’d on the 17th. Fertility friend says I’m 9dpo.

So I’m either 7-9dpo and I really want to test, is it worth it?

I have about 10 internet cheapie test. With my first I had a faint faint line at 9dpo and a decent faint line at 10dpo.