Talk to Dermatologist on Skin Problem

i have a black spot on my back its size is around half inch or less its been from 2 or 3 months and its increasing slowly and the skin there is swelling there is no pain but it seems like the inside of the skin is damaged but from out its just like a black spot with swelling on it . some of my family members are saying its because of not sitting right and some are saying its infection but i think i do workout at home so there should be some exercise that i had not done correctly and thats why my muscle get stretched my family members said to apply Mycitracin on it but i am not sure what problem i have