Light weights, high reps is certainly not the way to go. Which it sounds like you know.
And I will probably touch on this again later in this post. But I have the sneaky suspicion that your definition of "heavy" is very different than my definition of heavy.
However, your body just responds "easier" to weights. Not differently. Catch my drift.
Truthfully, it sounds to me like you simply need to reduce body fat in order to "lean out." It is tough to tell without seeing a picture, but from the words you are saying, that is what it sounds like to me.
Let me also say this. You don't add appreciable amounts of muscle without being in a CALORIC SURPLUS. If you have found yourself growing big, bulky muscles with ease, especially being female, you are eating over maintenance.
Diet/nutrition controls the way your physique responds to training more so than training in and of itself.
Ahhh, just as I suspected. You are NOT training heavy relative to my definition. Heaviness or weight dictates rep range. The heavier you go, the less reps you can perform, and vice versa.
That said, my definition of heavy dictates a rep range of about 4-6.
Before we get into training splits and periodizations, I would also like to know your stats (age, weight, height) and how you've been eating. Honestly, from where I am sitting and the knowledge I have from working with A LOT of people, your problem lies in nutrition more so than anything else. That is just a guess though, without knowing more at this point.
And before you reply, I suggest you read this workout I posted to get an idea of the type of training I am talking about:
http://weight-loss.fitness.com/weight-loss-through-exercise/11048-workout.html
