If someone could offer advice I would be thankful ❤️

I’m currently on my first period since having my daughter— 20 months ago. Before baby, my cycles were a little longer but mostly regular I think (sorry, I didn’t really track my periods a whole lot and I don’t remember much) I’m not sure what my cycles are doing these days bc it’s my first period. I’m on cycle day 4.

What day do you think I should start doing OPKS? Cycle day 10? 14? What day would u start tracking if you were me?