Period days got shorter? Please read/help

I’ve been havin my period since like 6th grade. I’m 20. My periods have always been heavy an for 7 days. Always. And is usually a 21 day cycle.

I just started becoming sexually active in March, stopped being active around the end of April. I am not currently sexually active. I took plan B once both months.

I don’t remember having a period for may or June because my phone was broken an I couldn’t log it. I was stressed/life changes at the time so that could’ve been it?

My period for July was med for 4 days an spotting the last two.

On day 2 of my period for this month and it doesn’t seem super heavy like normal. Ive been testing neg this whole time. cycle is now averaged at 34 days.

Could this be plan B still? Hormonal? pregnancy ?? Thank you for the help.