Red, rough patch

Hey mummies and daddies. My LO have this red patch on his stomach. And now the whole tummy area is red. This morning when I went to change him his red patch area is kinda hot and his belly button is slightly darker. When I went for his 3months check up (2 jan) the doctor said it’s dry skin. But I’m just thinking dry skin will cause heat and redness on it? Has anyone experience this before? And how do I cure it?