How much muscle should I expect to gain?
The average weight training athlete, if using the proper diet and training program can expect to gain 1.5 - 3lbs of lean muscle mass per month. This number tends to rise of course when you start to factor in genetics, supplements, recovery time, etc.

Determining how much muscle you could possibly gain can be gauged by several factors. First and foremost, your genetic potential, how much you eat, what you eat, how hard you train, and your training experience all play a role in how much muscle you can expect to gain. First, your genetic potential plays a huge role in muscle gains. Some people known as hardgainers will have to try very hard to put on even a pound of muscle. And then there are those who were blessed with the genetic ability to pack on muscle with ease.

Secondly, how much you eat also dictates how much weight you gain. If you are barely consuming enough calories to support your new growth, odds are you won't gain very much muscle at all. Make sure you count your calories and know how much you are consuming. Next, what types of food you eat is very important. You could be eating 5,000 calories a day of fast food and cookies and then realize that your not making good gains. The answer is obvious, to make good gains you have to eat good food. This means getting a lot of high quality protein, complex carbohydrates, amino acids and fats. Of course how hard you train also determines what kind of progress you will be making, your muscles wouldn't grow very much without it. Training hard doesn't mean you have to be in the gym 24/7, it means going to the gym anywhere from 3-5 days a week and training the right way for your athletic type, whether it would be an endurance athlete, a bodybuilder or someone trying to lose weight. Lastly, your overall experience will play a role in your muscle gains. Beginners tend to put on muscle quickly and easily, especially when coupled with an advanced diet. Then as you get more into the intermediate and advanced stages you may notice your gains start to taper down.

What is overtraining / How do I know if I am overtraining?
Overtraining occurs when you train your body beyond its ability to recover (its so-called recovery-ability). If your body cannot recover from the last workout then it will be unable to adapt and unable to grow. Symptoms of overtraining include:

1. A higher-than-normal resting pulse
2. Illnesses become more frequent and last longer than usual
3. Muscle spasms while resting e.g. eyelid twitch etc.
4. Shaky hands
5. Loss of Sleep
6. Loss of appetite
7. Unexpected and unexplained fatigue
8. Unintended weight loss
and MOST IMPORTANT OF ALL
9. very slow or nonexistent gains in exercise poundage's in the gym; i.e. static poundage's or poundage's that are only a few pounds more than you were using months ago. In extreme cases, overtraining can lead to a loss of strength and the use of reduced poundage's.

Solution: If you are overtraining on your current routine, then cut back on workout-days per week, and exercises and number of sets used. Best of all give "The Hardgainer Method" a shot for 6-8 weeks just to see what you are missing. In most cases the person who tries this for the first time will experience a rapid gain in strength and muscle mass, along with an increase in energy.