No flowers on my blueberries

I have three, four year old blueberry bushes. They have flowered every year although thanks to the birds my yield has been small (one berry each of the last two years...please, don't ask). They This year I had zero flowers on any of the bushes. Not a single one. Zero. Zip. Zilch. Nada. I thought that maybe it was the weather but the guy at the farmers market where I was buying blueberries (aarrgghh) was excited to tell me what a great year this is for them. The only thing I did differently this year was to fertilize with Hollytone which I did at the recommended time and amount. They even flowered the year after I transplanted them but this year...

Any ideas? Remember, misery loves company and I'll feel less like an idiot.

Are they in full sun? What is the soil pH? Mulching every year? What are the varieties?

The variety is Northland. I haven't tested the soil pH but the plants are near an azalea and we have rhododendrons which are healthy so I assume that the soil is acidic. As well, the plants have bloomed in previous years. They get at least 6 hours of direct sunlight and then dappled the rest of the time. I didn't mulch this year but they were mulched last year. The only obvious difference is that I fertilized this year. I have fertilized before with a product for rhododendrons but not with Hollytone. If they hadn't flowered each year before this I would just think that this is my usual pattern. But for all three plants to fail I figure I must have done (or not done) something.

escu, I am far from expert but will take a couple of guesses here. My blueberries get full sun and I usually do not fertilize (I probably should). Every year I put a 1-2" layer of peat around them. So far, blossums and flowers and fruit every year. (this year, huge fruit!) A couple of years back, I bought a cheap multi-soil meter at the local nursery. Paid under $20.00 for it and has been well worth the money. Sure it's not completely accurate, but it does give a pretty good idea of soil pH and other things. pH for blueberries is very important.

Second consideration is that if they are all Northland, then you would probably get a lot more fruit by supplying a different variety for cross pollination. This does not help with the "not flowering" problem, but would help produce more fruit when they do flower.

Third consideration is that if near other plants, have the other plants grown enough in the last two years to increase the amount of shade your blueberries are getting?

Fourth consideration. If I am not mistaken, blueberries do most of their flowering and fruit on new growth (at least that's what it looks like to me). If your blueberries did not grow much last year, it would be normal to expect no flowers or fruit this year