REALLY NEED ADVICE ON THIS!!!!! (ARMPIT PROBLEM)?

I'm a 17 year old male, who is constantly sitting or lying down at the computer. I hardly do any physical activity. But for the past 2 weeks, I've noticed a very mild (sometimes sharp) pain in my armpit area (around the pectoral muscle area) that comes and goes. I mostly experience this pain at night, during the day I hardly feel anything. There is no swelling or other symptoms, just this pain. What could it be? (If it helps, I've had this persistent cough, which I got after a flu, and it gets worse when exposed or inhaling cigarette smoke, if any of this may be related). I went to the doctor, and he checked both my armpits, and said I may be allergic to the deoderants I'm using, and gave me a cream to use, which has not worked or relieved the pain in any way.

How often should I work out my pecs?

I found a great Pectoral workout where I work each muscle in the chest. I do three sets of 12 reps of regular knee push ups (equaling 36 push ups) after wards I elevate my lower body onto my bed leaving my upper body (waste up) dangling, and do push ups to the ground, three sets of 12 reps (also another 36 push ups) Then I finish the workout with another 3 sets of knee push ups of 12 reps EXCEPT my hands are at shoulder width, targeting the inner pectoral (for a total of108 push ups). I'm 15, 5'11 and weigh 141 pounds. As you can see, I'm skinny. So how often should I do this workout? Once a day? Every other day? I'm not sure. :/

What is the name of this disorder?

Where one of a male's pectoral muscles intact while the other looks like it contains more fat or something where it represents more of a woman's breast? Also, is this disorder linked to any neurological disorders?

Pectoral muscle spasms? more inside?

Try eating some bananas for potassium. Adding salt to your food and taking 1/2 of a multi may help, and stay hydrated.

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What did I do to my shoulder?

I was working out the other day and I was working with the Pectoral Fly machine. I'm pretty sure I did something to my shoulder. It hurt really bad, kind of crackled, and my fingers got tingly. Since then, it's been really sore and I can't really do much with it. I can make a fist and I can still move my elbow and my shoulder. It just hurts, and it's really sore. I've worked with the machine before without this happening; I'm pretty sure I just did something wrong this time around. Any thoughts on what I might have done or how (or if) I can fix it on my own?