My skin started having white spot on them. Now they are spreading. Can you tell me what they are? What should I do? Spreading on my arm and shoulder ever since I gotten sunburn.

Hard . Hard to tell without a clinical history and picture. Perhaps you have tinea versicolor? I would recommend you see a dermatologist for diagnosis and treatment options. I hope that helps a little.
Proper diagnosis. The rash could possibly be pity raisins alba. It is important to know the difference as far as therapy is concerned. Pity raisins alba will go away on its osm whereas t. Versicolor needs treatment eith an anti fungal see a dermatologist for proper diagnosis.