Could be arthritis, could be any number of things. If it's possible to do exercises that don't aggravate it, do them but since it seems like it hurts most of the time, it would be wise to find out what's wrong with it.
I have intermittent aggro from my lower legs, occasionally, where it feels like someone struck the top outside edge of the fibula with a hammer and then its painful to take every step when walking; yesterday it acted up but today it feels fine, if it became the norm, I'd be at the docs asking for a check-up though. Mine is like yours, nothing causes it, it just occurs.
36.5 kg /80.3 lb Middle-Finger DL (right hand)...