Brown period again??

So last month I posted about having an all-brown period. It came on the day it was due and I hadn’t had sex since before the period prior. However, this month my period is brown again. I made an appointment with a GYN on Tuesday, but your girl is panicking. Is it worth it to buy a pregnancy test before Tuesday? Also for context, tmi, but the consistency and color has been like average brown blood but like only for a day and then it lightens up again. I used light tampons for one day and now I’m basically free-bleeding. This month I experienced period symptoms like cramps, mood swings, cramp-related nausea, and headaches which is typical for me. I am on birth control and have been for about three years or so for abnormally heavy periods. Please help me put my mind at ease.