when should I test

I had my son 6 months ago, went on the pill at 6 weeks post partum and breastfeed exclusively. (although have added food now)

My period came back at 8 weeks pp.. And I had 3 periods that were regular and then the rest have been a couple of days out. I use an app to track it so it's about as accurate as can be.

I have taken the pill late a couple of times because life. My period was due nearly a week ago (on the 2nd) and it's still not here... I've taken a couple tests, but my cycle averages put at 23 days so it's still not been 4 weeks. When should I test?