When should I count dpo?

So I had a super weird fertile window and had 3 days of extremely strong OPKs. Cd 17, cd 18, and cd 19. My OPKs started reading negative yesterday cd 20.

When I had posted a few times about the confusion, I had a few women telling me that as of cd 18, I was 1 dpo. But I’m not sure if I should be counting from cd 20, or cd 18. It makes a bit of a difference, being 4dpo vs 2dpo.

I’ve had cramps since cd 10, which I had a positive opk on, but I was told it was not the day I ovulated by a woman on here. My cycles are normally 33-35 days however last cycle my period was 5 days early and only lasted 2 days.

So I’m really not sure where to go off of and I don’t want to start testing every day because as we all know that gets expensive