I agree with the advice to consult a specialized doctor if need be. I always like to read up on the condition as much as possible, so I can decide if I need to consult a doctor, and if so, more easily follow along with the doctor and ask (somewhat) educated questions. Also suffering from some hyperpigmentation, I came across this article: [ Link under review]
Definitely worth a read, particularly the section about safe alternatives for skin lightening. I hope this helps!