When to test

Katt

Hi guys. So last period 11th October. My periods are literally confusing the heck out of me. 26 days then 31 days then 28 days. So I don’t even know when I ovulated or anything! I doubt I’m pregnant. I mean highly doubt it. But when do I test from the 11th October. I’ve got first response at the ready. So what day should I start. So confused my brain don’t work.