Can u please help me i have this black spot on my face and its bad?

can u please help me i have this black spot under my bottom lip from when i had a very bad cold and i been over that for 3 goin on 4 weeks now but i wash my face everyday and my mother told me to put some petroleum jelly on it and i been doin that everyday and ppl are startin to really notice it and im getin really really embarred so i just cover my face when i see ppl cuz my family, friends, and even strangers notice it and when i was in the store this women said ( hey u have something on the bottom of ur lip) which im even more embarred but i dont know what to do its been there since my cold came up ... what can i use.