Is it best to brush 2 or 3 times a day if enamel is eroding?

Depends. Enamel is constantly under attack by the acids that are inherently in your mouth & from the foods & drinks that you consume. Your saliva helps buffer the acidic levels in your mouth. The best time to brush your teeth is when the ph in your mouth is neutral, never immediately after consuming something acidic. First rinse off your mouth thoroughly with water. Ideally, use only a pea-sized amount.