When Can I Test?

I don’t really know when I ovulated this month. Roughly around CD14-16 ( Dec. 11th- 13th) and I’m on CD21.. I’m suppose to start on the 28th. Since I don’t know when I ovulated this month, could I test like 3-4 days before my period and test positive? Or would it be too soon still? I mainly want to find out so early because it will be Christmas.

Thanks in advance!!