Late starting period lasting only 3 days

Hey ya'll, I'll start off with I already have a doc appt in the works but due to the weekend and holiday getting in the way it'll be a while till that goes through. Anyhow, I was hoping to see if anyone had personal experience with my current situation since I can't find much online myself.

So my period started 3 days late and only lasted 3 days. First 2 days were extremely heavy (i could feel thick clots) and out of the norm and the 3rd day was practically non existent. By the 4th day it was gone. I never leaked either, only when I used the bathroom did anything come out.

I do have hypothyroidism and I've been on meds for it for a little more than a year. Not sure if that could be a reason. I'm afraid it could be Endometriosis and based off the check list it very well could be. My doc agrees which is why I was immediately given a gyno referral (appt I'm waiting on) I've never had a period like this before. I've always been fairly regular, except for the one period that helped diagnose my thyroid issues (it showed up 2 weeks early) but aside from that period a year ago in July and this one, I'm regular (maybe a day early or late from the glow prediction but that's normal).

Anyway if anyone has any personal experience with this and was successfully diagnosed with something I'd really appreciate the heads up of what I could possibly expect. Thanks ya'll.