why does my main fuse keep blowing everytime i try to jump start my mazda protege

The most common reason, as stupid as it sounds is having the jumper cables or battery in backwards ( negative wire connected to positive post). If it blows when you turn the key, not when you connect the cables you could have a short in one of the wires to the starter. Starter wires get brittle from heat and oil and often get damaged while changing the oil filter due to their close proximity.