You might ease off on the fertilizer--too much nitrogen can stimulate lots of green growth at the expense of blooms. Out here there are some places where they grow them on those cement walls along the side of the freeway and I doubt they get fertilized at all but they bloom like crazy.
I googled "trumpet vine wont bloom" and got a few answers earlier - I was on my phone so I couldnt post. But maybe try that.
It did say not to fertilize them in two of the articles - and that it can take up to 10 years to bloom.