It sounds like a virus if it's inconsistent like that. I would just rest and re-group. These things tend to happen when you try to take on more than you're used to.I have had an off and on sore throat for the past week. It goes away for a few days then comes back. I can't figure out if it is sinus related or some sort of low-level virus I'm just working on kicking. The days I have it, I feel so blah and lacking in energy.