I think you already know what the answer is.
Sore muscles are a sign that they need to recover (repair & rebuild).
I know how you feel though. Sometimes, being consistent in training is about creating a mental state that borders on "addiction". A lot of us go through the same thing, e.g. my leg/arm hurts, I have a cold, I feel sick, i'm exhausted - should I train today?
Just remind yourself that training can hinder your recovery sometimes, and that your body needs adequate rest periods. Rest can be just as beneficial as training.
A compromise would be to make it an "easy training day". E.g. spar with a beginner and go easy, or just cardio, or just footwork, etc... Whatever doesn't exacerbate what already hurts.