Ulcers in OTTBs isn't uncommon at all.
Also, if you have a big 60cc syringe from a vet (though a small one from like Walmart will work, just a bigger pain to give), give him 60ccs of Pepto-Bismol once or twice a day. It works the same in horses as humans, so it'll make him feel better. It won't heal obviously, but it'll ease their tummy ache.
You could talk to your vet about a product called Draw. It's meant for cleaning exterior wounds, but the main active ingredient is magnesium, so it heals ulcers too. My vet gave me that. My mare got 60ccs twice a day in a little bit of grain (so she'd eat it). Cleared them up in a month for $80. And since I don't have a trailer and the clinic is over an hour away, she used Abby's symptoms, personality, and some acupuncture to determine ulcers. Random, I know, but it worked.
GastroGard is magic, like stated before. You'll notice a difference in two days, it's just extremely expensive. Also, starting him on U-Gard after he heals up could keep them from coming back. My BO uses it on their show horses and swears by it. Abby was started on it last week. It does take about 3 months to take full effect though. Stateline has it the cheapest that I know of.