I think I have something wrong with my shoulder.
When I drive for an extended amount of time ( a couple of hours ) - I drive with my left hand - my left shoulder hurts.

I can crack my shoulder by holding my hands behind my back and pulling. Sometimes my shoulders crack by thereselves if I'm pulling something downwards.

If I'm writing on the wall board in class and I'm writing at the top of the board my shoulder gets tired relatively fast from the lifting of the arm.

I have well developed shoulders so I'm thinking may be I have an inner muscle that is weak or something.

If I'm doing triceps extension to train my triceps ( where you hold a dumbbell over you head in one hand and bend ur arm and then lift the weight) holding my arm high hurts my shoulder even if i'm holding a light dumbbell. Also if I'm doing bench press when I'm really working hard sometimes when lifting the weight my left shoulder hurts.

Any advice would be appreciated. Thank you.

stop all activity that hurts and go see an orthopedic doctor.

I did see a specialist 2 years ago, he said there was nothing wrong and that it was probably from all the studying (the pain was constant during my time studying for my finals - no work out involved but a lot of sitting on a desk with arms on desk. - )

The doctor just made me do some stuff no x-ray photos are or anything.

To me, the shoulder is the most problematic body part, it's so complicated due to its great range of motion.

I would do the basic shoulder exercises with weights that you can do at least 10 reps -- use your best-feel judgment, just not on the heavy side. Don't expect immediate, like tomorrow results, but in two or three weeks they should be better. I don't know the names of these exercises but they must be all over the web. Flies, etc. from all orientations...

Your history of having similar shoulder pain two years ago and that it was not associated with any upper limb activity suggests that it may have originally been either a nerve root irritation coming from the neck (constantly being bent over books/computers studying can cause cervical discs to put some pressure on the nerve surrounding them) or impingement of the rotator cuff (resting on elbows and hunching over can cause shoulders to ride up impinging the shoulder muscles)

Your current problem may or may not be related to the old one.

Nerve related issues often result in the limb feeling "heavy", a decrease in reflex response and you may or may not have paresthesia and pain. Here's a quick check to see if it is coming from your neck. Lift up your arm to where it feels "heavy", then get someone to get hold of your head holding near (under) each ear and gently pull up and hold your head with a little bit of traction (obviously ripping the head off is not going to help!). If it is nerve related you may feel that your arm feels lighter.

If there is no change in symptoms it might be a "rotator cuff" problem. At certain angles an impingement can occur on the muscle resulting in pain and weakness (impingement pain can also be quite sharp with sudden movements) or it might be that the rotator cuff muscles are just weak (seeing as you have a long history). There is plenty of literature about exercising these but keep in mind that they are stabilizing muscles and so your workout should aim to improve endurance rather than just going for strength (after all, your main problems are related to sustained activity above shoulder height).

Of course you could also have a combination of both or something else altogether (bursitis, labrum tear etc).

Your best bet is to see a physiotherapist, chiropractor or other similar health professional who will be able to assess as well as treat the neck and shoulder, and also give you the appropriate exercises.

This is one of those tricky ones that is best done with a face-to-face assessment.

Good luck!