when should I take a pregnancy test?

Kayla • Recently married, 2 beautiful girls and 1 on the way!
I'm on Metformin and the past couple months  I have started on the 12th like clock work!! Then this past cycle was the 18th!  We decided to not do opk's this cycle and just have fun, so I not sure when I would test! But roughly a 35ish day cycle? What do you ladies think? Opinions?