I think the spot would take a lot longer than one day to come about. You probably have not used a good broad spectrum sunscreen throughout your life. Most people haven't so don't feel bad. The spot should not get hot and burn when you are out in the sun or heat now. I would recommend you seeing a doctor because there is probably something else going on as it shouldn't feel any different than the rest of your face. Tell the doctor that is feels like it is burning and hot.
Hydroquinone is very harsh. A vitamin C serum will lighten the spots if used every morning.