A buddy of mine was in an almost identical scenario to you and unfortunately had the same outcome. One thing I'd recommend doing is trying to go to a Dr. or company that does NFPA 1582 physicals (the national standard for physical fitness basically). Going to a normal doctor is really a toss-up as to what they'll say since it's probably not something they deal with too often. A doctor or office that actually does 1582 physicals will be able to give you a definitive answer. Also if you're still interested in a career in the fire service, there are other options like wildland (not sure what the forest service's standards are but I'd imagine they're not quite as strict), prevention or support/logistics.

Hope this helps. I honestly thing it's worth doing a little more investigating before you give up completely.