Hydrangeas flower on 2nd year wood so the pruning definitely will be to blame for a lot of it. If you have to prune it then only prune 1/3 this year, 1/3 the next and the other 1/3 the year after; that way you should have enough 2nd year / older wood to flower.
Also, when I was at Hampton Court Flower Show this year, I commented to a hydrangea stall owner that one of mine that I bought two or three years ago wasn't flowering and he said that from April onwards to once a week feed with Tomarite as that encourages flowering. I've got quite a few hydrangeas in my garden and four aren't flowering at all, whereas the others are doing OK or very well. Needless to say I'll be stocking up on lots of Tomarite for next year