Is anything in your life that presented itself in the last few months that didn't exist before? That was a kind of clumsy sentence...what I mean is, have you taken up a new activity, or a new job that has changed your general mobility? New exercise routine? New bed? New favorite chair? Consider all those types of factors first. Also...which joints? Or most of your joints in general? There are so many factors to consider, but if it's something that just recently popped up look at what else might be new in your life, the chance of correlation and causation is usually more probable.
Is it indicative of a serious problem? Impossible to tell at this point, over the internet, with no other knowledge of your background, age, training history, and the like. In the meantime, consider trying some extra stretching routines, maybe a little yoga. Pay extra attention to your ergonomic situation (i.e., how your body functions within its environment)...even weird little things like a new backpack, new car seat, new shoes, or anything that might force your body to make an adjustment even if it's not something that catches your attention immediately.
If you're really worried about it, make sure to do some research on a doctor before you go -- more often than not, a physician's knowledge of nutrition and especially sport-related nutrition comes from what they study on their own outside of medical school. You can sometimes tell approximately what year a doctor graduated from med school based on their immediate comments on nutritional matters. Look for an orthopedic surgeon with sports medicine sub-specialty.