It's not at all unusual for people with gallstones to develop pancreatitis. If a stone gets lodged in just the wrong place in the ducts, the pancreatic enzymes can't drain properly to the small intestine. The result is that those enzymes, instead of digesting the food you eat, they end up digesting the pancreas itself. On top of that, the pancreas is one of the more delicate organs of the body. Once it gets disturbed, it tends to keep complaining for quite some time. Does that mean it will never go away? Not at all. Because your initial problem didn't reside within the pancreas itself (like a tumor or a pseudo cyst) your odds of a complete recovery over time are much better.
Age has nothing to do with pancreatitis. Matter of fact, the biggest cause of pancreatitis is alcohol. Sadly, many chronic panc patients here in the US are treated like dirt because the nurses and doctors assume they're alcoholics. I'm sure your doc has already told you, but for anyone else reading, alcohol is 100% off the menu for pancreatitis patients.
Don't let the word "chronic" scare you. Roughly speaking, acute means only sudden onset. Chronic, in your case, means that you've had it for a while. It takes time for the pancreas to settle down after an acute attack, so the usual treatment is to avoid alcohol and rich fatty foods while treating the pain and nausea with medication. You're so young that you will very likely recover just fine as long as you mind what you put in your mouth and let your pancreas rest and heal. It's not going to happen overnight though. :-)