Do I really need to change my antifreeze in 3 months ?

If you are going through coolant that often you need to find out where it is going. Do you have a coolant leak or a blown head gasket? Check your oil first to see if you have creamy tan colored oil. If it's tan it has water in it and you need a head gasket. When you top the radiator off again and you can use water to test it run your car to get the engine up to normal operating temp and then park it and open the hood to look for leaks. When your driving look for white smoke coming from your exhaust also which would mean head gasket. By the way your friend doesn't know automobile engines either if that was their answer.