HELP! Gum is brown between my two back teeth!?

Now before you tell me to brush me teeth, I already know that I should. I'm not perfect and with a busy schedule during the day it's hard to remember to brush my teeth at night. I always brush my teeth during the day, and occasionally at night (maybe 3-4 times a week at night). The problem is that I've notice a slight brown discoloration of my gums in between my two back left teeth. I would like to tell myself that its my wisdom teeth, since I haven't gotten them pulled yet, but it just might be a cavity. What do you think it is and can I wait a while to go to the dentist? Does this make me a disgusting person lol