Tri Time

I'm already getting excited for the triathlon season for the year. I'll admit, I like short triathlons way better than I like running. I could ride bike and swim for a long time. But the running, now that is a different story. I've been going to spinning classes one time a week (in addition to running and the elliptical) for the last few months and I am thinking maybe I should increase that to two times a week. That is the one thing I don't really understand....how to know how much of something I should be doing? I was lifting weights for a few months and loved it. I am one of those people that if I'm going to lift, I'm going to lift a lot. I don't like doing the 20 lbs. for 30 reps or really doing burnouts. However, I have now stopped lifting because my legs were getting too big. Okay, not that I'm a powerlifter or anything but my jeans were not fitting as loose in the thighs as they were before! Does anyone have any suggestions on this? How do you know how much you should be lifting? How do you know how much you should decrease the weights so you don't bulk up? Now that I have gotten my tax refund, I'm thinking maybe I should hire a personal trainer because I also need help understanding the zones for heart rate monitors too. How confusing! Anyone had any experience with this?