J., I have to agree with those who posted that this is normal.
We're told that there are kids who "sleep through the night by five months and are perfect sleepers from then on" and a ton of other fibs. Children's sleep patterns change and change again. And a child with issues like asthma and reflux has never really known solid sleep. I have to tell you -- and you won't want to hear this -- that even when her issues get resolved and all her teeth are finally in, her sleeping patterns will still change. My child is eleven and her patterns change during the year, the season, etc.
I know this is not very comforting. I know you're searching hard for reasons for her wakefulness--because concrete reasons are things we can "fix"-- but there are not always reasons. Just keep going to her. I do not believe at all in "cry it out" methods; they only teach a child that "when I cry, the adults I trust do not come" and that breeds insecurity; it does not "teach" the child anything positive.
She truly will not be doing this forever though it seems like forever to you right now because YOU are sleep-deprived. But continuing to seek concrete medical or physical reasons (ear infection? teething?) may only frustrate you. If she is tugging at her ear, touching it, etc., then yes, go to the doctor. If other teeth are coming in, yes, teething could be one part of it. Nightmares are another possibility (she is not too young for them). But you may just be driving yourself crazy trying to find a reason and a solution when the only reason may be that she is 18 months old and needs you. Do continue to do what your doctor said and go to her.