When should I start testing?

Hi ladies i been trying for 4 years now i have irregular periods (every 3 months)i went to my doctor and she wants me to take ovulation test to see if I am the problem maybe I don’t ovulate normal.So she made me go on the pill to have my period every day.So she told me to use ovulation test but I forgot to ask when should I start testing. To I test right after I get of my period ? And should use my morning pee or what time should I test? Also how to I count when I ovulate the most ?

Currently on my period day 3 below shows my 3 periods on the row 👇

It feels weird getting my days every month now