Thanks for writing. I wouldn't necessarily assume the plant is not flowering because it's hungry... More often than not, there's something else going on, and in some cases, fertilizer can make it worse.
So first off, I'd take a look at the growing conditions. Is your plant in full sun with well-drained soil? Shade, wet soil, or moist, heavy clay can set the plant back. Do you water it much? If so, it might be getting too much moisture. Pruning it too hard can also reduce its ability to bloom well.
If those factors don't seem like they're it, then I'd do a soil test to see what, if anything, your soil is lacking. The results of the test will tell you what products are best to fertilize with.
---Justin, Senior Garden Editor, BHG.com