We had a DC on the old forum for a time and he would say that it only takes 3 or 30 grams?? or milligrams?? {can't remember the exact amounts} of pressure on a nerve to start causing a symptom.

So my guess is that something is starting to put some pressure on that nerve. Since it is just starting to happen now is the best time to try and head it off.
If you can use the anatomy links {in useful sticky} and maybe track that nerve to find out the best stretches or postures and relaxation moves to help release that pressure or run it by a expert PT or DC if you have found one near you.
Of course try not to do anything that will worsen or aggravate it.