help needed

[msmary]

I am short and have recently started running, I joined a club and have a running program to follow. I soon will do my first half marathon. The only problem is that my lower body has become way too over developed, my clothes are actually getting tight. It is muscle, but more of a bulk and less of a tone or leaner muscle. I do work out with weights about 3 times per week concentrating on a body part each day. Since I started running for a longer period of time, I sometimes do weights the opposite dat of my cardio, where as before I did cardio and weights on the same day, do you think this may be what is causing the bulk? The only advise I got from others was to make sure I do lighter weights on my legs and that running won't make the leg muscles bigger. I hate to stop running since I have come so far any suggestions would be greatly appreciated