definitely sounds like your horse is just displacing. Talk to your vet, and if there's a clinic nearby, i'd go have either tie-back, tie-forward, or laser procedure done. Considering, it's a fairly cheap and very easy procedure, and they only about 2 weeks off from it. It's usually (depending which one you do) about an 800-1200$ procedure, depending on which you do, where you're located, your vets, etc, etc.
"A righteous man has regard for the life of his beast"-Proverbs 12:10-