Not all citrus are created equal; some like calamondin grow fast and produce quickly; some, especially mandarins tend to grow much slower and may take longer to produce fruit.
The most important thing, in which you have erred, is that when you plant a citrus you should not fertilize it for at least 2 weeks, and maybe closer to a month. The absence of fertility causes the roots to grow in search of food; and after the roots grow, the leaves and branches will grow and then they need food.
I have experimented with Citrus Tone in my nurseries and have found it to be pretty hot; a little is good, a little more will burn a young citrus or maybe kill it.

I guess I did not mention that I have the tree for a little over a month and put about a teaspoon of Citrus Tone. The fertilizer idea was from the nursery from which it came. Hopefully I did not do any harm. After 24 hours it still looks ok, so I am hopeful.
When I re-potted it the roots looked like it was throughout all the medium it came in.
[URL=http://imageshack.us/photo/my-images/14/photo1ba.jpg/][IMG]http://img14.imageshack.us/img14/6875/photo1ba.th.jpg[/IMG][/URL]
Here is a picture I took of it a couple of days ago.

What fertilizer would you recommend & when should I next fertilize?

Thank you!

Lets try the image thing again.

http://imageshack.us/f/14/photo1ba.jpg/

Container growing is a world for container experts; and there are plenty here who can help you; maybe start a new thread with that question, or search the site using that little search box at the top right of the page.
I think you should fertilize about 4 times per year with a citrus fert that has a ratio of NPK near 5-1-3. I would also get a good foliar fert with micronutrients; I use Bayer Bayfolan Forte for my garden trees and apply it every 15 days; others here use Foliage Pro or others.
Some container growers or drip irrigation growers like to apply fertilizer every time they water... sometimes called "weakly weekly". Again, I have little experience with container growing except in my nurseries.