When you are fitting the pelham bit decide whether you want the single rein version or the double rein - but you might need help in learning to use the double rein version,
The head throwing could be
The fit of the bridle (eg tight around the ears) ,
The fit of the bit (too high or too low)
Or his wanting longer reins and more freedom from your hands - in other words he wants freedom to stretch his neck to go faster
Or maybe you are subconciously jerking the bit in his mouth (it happens)
Eventually, if you can't isolate the reason, you could tie him down with a martingale but it would be nicer if you could isolate the reason for the evasion.
Some horses have learned head throwing as a bad habit.