It's persistent, it's annoying and it needs to stop.
When it first started, it was just on my walks. More recently, however, the pain has been creeping into my everyday life. I'll be sitting in class or walking to my internship and suddenly, there it is.
Because I'm studying to be a criminal lawyer, I'm into finding the guilty party. I'm all about the who-dun-it, in fact.
The evidence points to two possible culprits: 1) poor walking posture and 2) weak abdominal muscles. I have decided, your honors, that both are acting in concert and should be arrested.
Ok, legal jokes aside - there is something wrong and I'm working to fix it. Already, I am seeing signs of improvement, too!

Throw your shoulders back, hold your head up high, perks the girls and WALK WITH PRIDE!
Then, when you are on your off days, work your core! Muscles balance each other, if you only work one group, you can throw things off balance and end up hurting yourself. All of the walking involved in training means you are stressing out a certain group of muscles. By working your core, you can balance the work load a bit. I use a stability ball to work my core - following a regimen designed by Women's Health to give me a bikini-worthy body. I also use it when I'm studying. I just sit on it - keeping yourself balanced subtly works those core muscles without you even knowing it!
Since I started working my core, I've noticed that the pain doesn't show up quite so much. Maybe I'm wrong and there is another culprit lurking in the shadows (if you know of a possible suspect let me know!), but in this case, correcting these other problems will only be beneficial anyway.
I rest my case.