I would say your best bet is to drop the third sleep!

DS is 14 months old and only just settling in to a sleep routine that I like! Since 6 months he has been waking every 1.5-3 hours all night long. Now, just in the last couple of months he has started sleeping much better. His first block of sleep for the night now ranges from 3.5 - 6 hours and that is MUCH nicer!

Hang in there and experiment a bit until you find what works!