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!