Talk to Dermatologist on Black Mark After Waxing

I got my bridal services done on 27th of December and It included the arm pits being waxed. after my underarms waxing it was hurting a lot so I lathered some petroleum jelly and the arm pit was red as well, however after a day it turned black/brown this is not how my underarms looked. now I am unable to tell if it's hyperpigmentation or a burn or a bruise. It doesn't hurt. it's been over a month now and it hasn't budged off and it's really bad. I would be extremely Thankful if you could tell me if it's a bruise or a burn because it's just black in colour without any pain or scabbing and what can I do to fix it since I have my rukhsati in a month.