Hello Sir,I Am Kkewal Vyass From Mumbai(india),I Have Becker Nevus

Hello sir,I am kkewal vyass from Mumbai(india),I have becker nevus on left side of my neck which is growing bigger an bigger it started with my swimming class the patch appeared at age of 13(2003) and it was small like a beauty spot but after 7 years that patch has reached near my jawline and has covered my half neck and if I apply any antopigmentation cream it get lighter but i get boils on it can you suggest treatment for this problem

Waiting for positive response.