Yes without sunscreen its not possible for me to go out in day time. Heat rashes and itching immediately starts and generally stays upto a week. Early morning and late evening are the best times to get out for me else indoors mostly.
I do find that the heat in hill stations and high altitudes affects my skin quickly than in plains. May be exposed closer to sun in hill stations.

I was trying to write an answer, but when I tried to move my screen up, my comments disappeared. I will try to hopefully give you a little hope. I will go ahead and say, that is is probably not that a Doctor that does not care, a lot of Doctors even in this day and time, have no clue how to treat Vitiligo. If the full truth was known, there is no cure. But, I could be wrong. I think the Vitiligo Foundation is located in Clearwater, Florida. I do not think they have answers. Please be careful if you contact them. At one time the Vitiligo Foundation had started in Tyler,Texas, then they moved I think to Columbus, Ohio, them to Florida. I pulled Clearwater, Florida up, says they founded it years ago. I am not sure. Years ago there was a magazine that went out about Vitiligo, but I have not seen that in years.. TTYL.