I encourage you to use a tracker app like Flo. It's very useful at all stages of life, especially in perimenopause when you're busy with life but need to accurately report cycle changes to your Gyn.
Take a pregnancy test. Get bloodwork, in case something crops up that might make your periods irregular, like thyroid disease or anemia. Think about supplementing with vitamin D, most people in the northern hemisphere are deficient and if you're starting perimenopause you don't want to make your bones brittle.