I think you should first measure yourself at home and use a few websites to assess your size.
Does your bra feel wrong? I presume it does otherwise we wouldn't be talking about it :P
Then go down to a proper underwear store and start trying out the bra's, to see which ones fit the best... Different models and different brands often require that we up or downsize.
If your bra does fit, if it supports your boobs, if they don't "buldge" over and/or on the sides and if the back part doesn't ride up... Then you are probably wearing the right bra.
http://youtu.be/BUVr8kUFmSc
I used to buy cheap bras and they wouldn't really fit me well... The wires would sit on the bottom of the boob and not on my "ribcage", so you could actually see the boob from underneath. That and they wobbled a lot, so not quick movements and I had the 4 boob issue... Then I discovered that there
are bra's for women with large breasts, and since then... My boobs look better than ever

The wire sits under the "fold" of the boob, not under the boob itself, they don't wobble so much and no more 4 boobs