Hi Georgia,
I really feel for you - I've had a LOT of experience with the early wakings. Carys was doing the same thing for a while - waking up around 5:15am or so. She had already gone down to one nap at that point too, and was taking it too early in the day (around 10:30am).
When she started waking that early to start the day, I had her take 2 naps again. The first one was usually pretty early - 8:30 or 9am, and the second one in early afternoon. However, doing the 2 naps didn't really help the early wakings. So we decided to go back to 1 nap - but at midday - and put her to bed earlier. She is now back to waking up between 6 and 7am (her usual wake time) and taking a long nap finally (1 hr, 40 min to 2 hrs). I'm not sure if it was because of what we did, or because she just was passing through a phase. I think she may have been waking early because her body knew that she'd get to sleep again in the morning, but then she would get overtired by bedtime. Her naptime is now around 12pm, and her bedtime is at 7pm.
Good luck!