My daughter is older than your son - 18 months - but she just went through something very similar. She popped out two molars and the diarrhea was done with. We managed the diarrhea though while it was going pretty simply with yogurt and bananas. We didn't give her too much fiber - no berries, cut down on peas, broccoli, etc.
Your baby is still small and may not eat those things yet. He surely can have banana and if you're timid about yogurt (it truly does help a ton, though) feed him RICE cereal. Don't give him any oatmeal or wheat - it will only add to the diarrhea problem.
I'm sure that it's teething, like you said. As long as the fevers are low grade I think you're ok. Good luck!