Follow you dermatologist advice. Don't self treat. Have patience. It should start depigmenting soon.

Very sorry to hear that u r suffering from vitiligo. Vitamin c or sour items non intake may not have much effect in results . Infact don't ignore a healthy diet. Nowadays Treatment options for vitiligo are plentiful with local application lotions and creams which are non steroidal and also UVB therapy can be tried under the supervision of dermatologist. Still if it's not recovering and no new patch is there u can go for cell Suspension Melanocytes technique which has very good results . Hope this is beneficial for u