It sounds as though he didn't used to be this way, am I right? When did the change happen? Last week... a few months ago... last year?
If it was a rather recent change, a week or two ago, I wouldn't worry too much about it. Give it some time and he may calm down. If it has been a long lasting change, consider that horses are very sensitive animals. You mentioned that you are "nothing but calm" on him. Perfect, but you aren't the only thing that may have affected him. What has changed recently?
1. Weather? I know where I am the weather just all of a sudden, within the last month, become amazing. Horses usually perk up in the summer months. He may feel his oats now that the sun is out.
2. New Feed or Feed Schedule?
3. New Turn-out Pasture, Turn-out Schedule, or Pasture Mates? Relationships between horses and changes within relationships affect their character under saddle.
4. New Barn, Stall, or Barn Mates?
5. New Tack?
6. New or Change in Work-out Regimen? Have you started riding him more or less, with or without a trainer, at a lower and greater intensity, etc?
The list goes on... search your brain for something that may have changed around the time he changed. See if you cannot either give him some time to adjust or return to what once was. If not a "new thing," your horse may need to be seen by a vet. It could be something as simple as his back's out of whack... this happens a lot to sport horses. He may just need an adjustment from a chiropractor. Having a chiropractor out would be a great way to have your tack looked at, too. As horses age and mature, their musculature changes. His tack may not fit as well as it once did.
Best of luck! I hope this was helpful.
Trainer, show rider