Always end up with toothbrushes that look like this? 
Chances are you’re brushing way too hard! Brushing too hard could lead to receding gums, which in turn exposes the root of your teeth and makes them much more sensitive to hot and cold foods. Gentle brushing with a soft bristle toothbrush and some care to floss afterwards is more than enough to keep your pearlie whites healthy & shiny!
P.S. Changing your toothbrush every 3 months is ideal.