Shortening periods?

I have an appointment scheduled with my OBGYN but they can’t fit me in until end of next month, so I figured I could ask here and see if anyone else has experienced this. I’m 28, I haven’t been diagnosed with fertility issues before, my cycles typically last about 28 days, almost on the dot. However, lately, they’ve been changing... I used to have my period for about 5 days after I had my kids, then about 4 days over maybe the last year or two, now over the last several months it’s between 2-3 days... Also, my period has shown up late a few times, like this most recent period was 7 whole days late and it seems like it might be over already, and it’s only the start of day 3... I’m not on birth control and haven’t been in years, I don’t take any medicines besides Zyrtec, I’m not that stressed and diet is okay. My thyroid is normal. I have two children and I understand the body changes, but this is starting to seem not normal? Has anyone else experienced this?