AB — one further thought to add to the great suggestions you’ve gotten —
If you’re building muscle without losing the fat on top of the muscle, you’re going to get bigger. The increased muscle mass will push the fat out and you’ll certainly look bulkier. What you need to do then is lose some of the fat while gaining muscle. I don’t know whether you want to lose fat or what your stats are, but if that’s the case, I’d suggest adding in cardio to your weights. Running, like Tig suggested, is excellent, as are walking, biking, the elliptical and anything else that will get your pulse elevated and keep it there and get you burning calories.
I’m hesitant to say this, but my personal experience has been that building muscle has only made me smaller. I’m 135 pounds but wear sizes 2 and 4 due to my muscle mass (most people guess that I weigh about 115 pounds

). A pound of muscle is considerable smaller and denser than a pound of fat, so you really do want to lose fat and add muscle to get smaller, in my opinion.
I'd like to refer you to a previous thread in which some of this is discussed
http://www.3fatchicks.com/forum/showthread.php?t=31893. In that thread, there's a picture comparing five pounds of fat and five pounds of muscle so you can see what I mean. Good luck and let us know how it’s going!