Talk to Dermatologist on Smelly Scalp Even After Fresh Wash

My sons scalp smells even if its freshly shampoo'd. He is just 2.5 years old. I used to use johnsons baby on his hair but then i noticed it made his hair noticeably dry, so i switched to sunsilk. He generally sweats a lot. His scalp is clear, no signs of fungus or dandruff. But i've noticed hairfall since a month. what to do?