Are you sure he is teething (red cheeks, sore bottom, swollen red gums) at this age they all start to dribble & chew things so it isn't a good indication of teething,
Also if it was teething I would think his day sleep would be bad too i think.
So my thought is it is time to move to 4hour Easy & get 2 long naps (2 hours) & one short nap (45mins). I may be he is getting too much day sleep & not tired enough for night