When should I test?

I'm wondering when I should test for pregnancy. Below I've attached screenshots of when I for my period is January and when I got it in February. My period is irregular so I thought I'd count the days in between jan and feb, and feb and March so I'd kinda know when I was supposed to get my period. From Jan to feb it was 37 days between periods and so far it's been 38 days. I still haven't gotten it. I hope this makes sense to yall. When should I test? So far I've had cramping and the last two mornings I've had very bad nausea.