M.F.
Please stop giving your child Benadryl unnecessarily just to try to get him to go to sleep!
It sounds like your son is overtired, which is why he's waking so often after falling asleep. Is he napping during the day? If not, that is probably the cause for the nighttime sleep disturbances. When children are overtired, they do not sleep well, but children who nap regularly sleep better at night.