Which procedure can help lighten dark skin on the back and buttocks? (photos)

Hi, my skin on my back and specially my buttocks are incredibly dark it makes me not wanna be inimate with anyone. It has always been an insecurity of mine and I'm too embarrassed to visit a dermatologist. i've tried using Kojic acid soap and then moisturize my skin with Eucerin roughness relief lotion and lock that moisturize with Vaseline every 3 days, it's been 2 months now and I haven't seen any result sadly. Would appreciate the help thanks you!.