I drink nothing but water and still have no energy?

See your doctor. There are many things that can cause a lack of energy or fatigue. This can include anemia, thyroid disorders, diabetes, etc. Best to see your doctor to determine the cause and provide you with a treatment plan.
Only water? But surely, you must already know that it is not at all healthy to only drink water? I mean, come on now. If you don't actually eat any food, you should know why you have low energy.

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Chest cold, cough, no energy, wheezing. Taking regular Robitussin (guaifenesin) and drinking lots of water?

Chest cough. You may have bronchitis or pneumonia so see your doctor for a possible chest xray and modification of your medication. You might do better with albuterol for your cough and possibly an antibiotic. Read more...
See below. Not sure what your question is, but with your mentioned history of wheezing and tobacco use, I would recommend you see a physician. As a general rule, most OTC cough medications (Robitussin) provide little releif, especially if you are wheezing. Read more...