Irregular cycles, when to test?

First time posting, but as the topic says, my cycles are irregular. Sometimes I have it and then a month later I’ll have it “on time” with an average amount of days apart, but then other times it’ll be months apart. My cycles have been irregular since I started getting my period, and I’m never really sure when is a good time to test (I still test though)

Some more info: I’m not on birth control, and my BMI is below average. I currently have not had my period in a little over 2 months and tests have resulted in negative