I've just started riding a quarter horse that's 10 years old and he's throwing his head - at first I thought it was the pasture he was in and that he was nervous because he had only been there one week. But I've brought him to my house and he throws his head - the woman I bought him from says he was ridden by the previous owner with a tie down. I've never used one - so I switched bits and bridle because the bridle they sold him with was very loose - and so was the bit. But even after switching he throws his head - enough to pop the reins over his ears if you let him.....any suggestions???