Persistant cough and cold

Anything that won't go away, needs to be seen by a doctor. In most cases you probably had a head cold that never went away that moved into your chest, perhaps became bronchitis. Either way you will need antibiotics to nip it in the bud which requires a doctors visit.

The black stool can be anything from too much iron in your diet (which is the most common case) to colon problems. See if you can track your deit to see if there is a pattern of very iron-rich foods like clams, organ meats (liver), beef, chicken beans. Share this information with your physician, but I doubt the 2 are realated.

Are you still experiencing other cold symptoms along with the cough? If it's just the cough, you should consider a really good expectorant. I would suggest Mucinex. It won't stop the coughing, but that's good because your body is coughing to expel mucous. What an expectorant does is free up the mucous so that the coughing is more productive. Once you've expelled what your body wants out, your body will return the favor by not coughing anymore.
As for the black stool, stool runs a gamut of shades based on the amount of blood and/or bile in it (a certain amount of this is normal). Dark stool is likely nothing to worry about, but black-and I mean jet black-could be a sign of internal bleeding. I know the temptation with these sites is to find reasons to avoid the doctor, but this is one of those cases where a doctor's vist is probably warranted.

I think everyone is in agreement- Go to doctor Melinda.