I was thinking the same thing, possibly teething. What I used during teething was a homopathic remedy for teething made by Hylands.
Homopathic remedies are non-toxic, can be used safely with no side effects.
Check your local natural foods store if you are interested. I used to give a couple of tablets before bed time if I thought that teething was going on. They don't always work for everyone. It might be worth a try. Also you can try using a cold wash cloth to chew on or a cold teething ring or something like that to ease teething pain.