I need some help about some technical issues

Hello, I wanted to ask you some issues about piano technique. I played the piano for some years, but really the only thing I focused on was to read the notes. I just cannot give changes to the volume of the music I play (I don't know how do you say "matices" in english). I have been trying to play fortes, pianissimos, crescendo, decrescendo, but everything sonds flat and forte most times. Also, playing Bach's inventions, for example, I realized that I cannot make every voice sound diferent, and give relevance to the voice with the melodic line. Another problem is that I don't like the sound I make, because it seems to me that I pound the keys, and for that, the result is an awfull sound with no delicacy at all. What can I do?? How can I put together the finger weight issue (I was told that one has to transfer the weight from one finger to another, mantaining the same weight always) with the issue of changes o volume (crescendo, decrescendo for example)? How can I do one thing without ceasing to do the other?? I will apreciate your advices very much!! Thank you!!