Its likely a deficiency, in which case the regular doctor will do little more than prescribe you a "bandaid" that will cause more side effects.
I would have a blood work up done, just to see.
I know that you say you are drinking "enough" water but be sure that you are drinking half of your body weight in ounces of water daily. (IE I am 130 pounds and shoot for 65oz water daily) Secondly pop, coffee, energy drinks and the like will dehydrate you. In addition to your daily water add water in for every one of those that you drink.
Salt, as mentioned, could be a culprit but less likely. Just be sure that the salt you are consuming is "Sea salt". The body doesn't use anything else real well. You can eat pringles and pickles until the cows come home and some of us, most, will not use the salt in these things.
It is most likely a calcium/magnesium deficiency or potassium deficiency.
Iron deficiency will cause extreme muscle pain in certain trigger points.
Adrenal fatigue can also cause muscle pain/weakness.
Any of these will need supplements to correct. Eating "enough bananas" isn't going to help you.
Getting a perscription for a pain killer is a very dumb way of masking what you body is trying to say... I hope you look into what you actually need! :)