That depends mainly on the height, and secondarily on a few other factors such as the gender. The commonly used measure nowadays is the BMI (body mass index); you can find an introduction here:...
No you do not need to lose weight. 120 is a good weight, but it all depends on how tall you are. If you are any where from 4'11 to 5'4 that is a good weight. If you are shorter you may need to watch...
If you use strength exercise to increase your muscle tissue, you will be heavier (all things being equal) because a given volume of muscle is heavier than that same volume of fat. However, if you are...