Positive OPK

I got a positive OPK Friday the 14th and again Saturday morning the 15th. I tested again Saturday night and it was no longer positive. I’m just wondering based on that when would I have ovulated? I’m trying to determine how many dpo I am but I don’t know what day I’m supposed to count from.

Sorry I am new to OPKs, still trying to figure out how they work!

Thanks in advance! :)