Thanks to all of you for the conversation, ideas and thoughts! Not sure about the nap schedule, since DS on an average day has as little as 3-4 twenty minute naps!!! He yawns and rubs his eyes a lot thru the day, telling me that he's still not getting enough sleep.
My gut tells me it's either these pesky teeth, or as first suggested, perhaps a lack of sleep??
He had a late night last night, since we had to wake him up to get home from an outing, and slept in til 7.20am this morning, so maybe I need to try and extend his bedtime? I still think he needs more daytime sleep tho' in order to achieve this, since he is usually beside himself with tiredness by the time bath & bottle rocks around between 6 and 6.30pm. If only he could talk and tell me!!