My LO went through a terrible period right before 18 months (from about 14-17 months, I'm thinking??) where she woke up a lot more than she had previously. But from about 18 months until recently, she's been doing really well, provided there are no illnesses, overtiredness, teething, etc. Really well for us means only one or two wake-ups a night. I know all babies are different, but maybe if nothing else works you will see a bit of a break around 18 months. We've had 6- to 8-hour stretches on occasion lately, some of them even in her own bed. Now, when we have those good stretches, DD decides to wake up at 5:30 or earlier -- but we'll work on that one later.
You mention you don't think it's teething -- I've learned to stop looking for answers, and just blame almost everything on teething! LO had 4 teeth poke through over about 6 weeks, so it's hard to say how long they took getting to that point.