Teething aside, it is often overtiredness that causes night wakings and early wake-ups and your lo sounds like a likely candidate! I cannot speak for wake-to-sleep, as my experience was that DS just woke up earlier!! I have hardly ever managed to get him back to sleep, and the most I have ever done is allowed a very early cat-nap of 30-40 minutes at 9am to tide him over - but generally I just give snacks and distraction until an early lunch and sleep!
I would really work on pushing the nap back, as he is only taking the one that is all you have to work on. If you can't go cold turkey and force him to stay awake until a later nap time, you will need to gradually push the nap back in stages, but at the same time bring bedtime forward as much as possible. You may have to live with the early mornings just until you have sorted his nap out and he is sleeping a decent amount, then you can move bedtime back again.
If you check some of the other threads out, most people have a great deal of success with early bedtimes, they stop night wakings and often help the early mornings too.
Sorry a bit gabbled, but something may help!
justine