Don't freak out. It might be something very minor.
Take a couple of rest days and then if it feels better, get back to the miles.
I know for me, I always have some odd pain going on in my lower legs.
One time, I ran 5 miles and afterwards I had this horrible pain in my achilles. I went to ride 30 miles and I could barely press on the pedal.
I rested one or two days... and it was gone, never to return.
Another time, when I was cycling, about 25 miles into a ride, I got this accute pain in my left knee. It hurt to pedal. I took 2 Advil, and poof! the pain was gone 15 minutes later.
Moral of the story: Sometimes we just get these odd pains. Back off and rest, and it will probably work itself out.
Good luck!
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"