It sounds like Erythromelalgia. Do an internet search for that and you will see that your symptoms fit pretty well. I have this, too. Go to your doctor and bring your research into the condition (most doctors are unaware that it exists) along with a list of your symptoms, how long they've been going on, and the severity of each one. There are some causes of this that can be tested for, such as diabetes.

You need to be especially careful not to get your feet too cold. Most of the complications of this are from frostbite from people putting their feet in ice water. Personally, I find that it makes the problem worse when you take them out of even somewhat cold water.

I find that stretching my Achilles tendon can help. Just kind of bend your knee and lean forward, stretching out the back of your ankle. Keeping my feet outside of the covers while I sleep keeps them slightly cold, so they don't itch. If you find that they are itching during the day, make sure you are wearing breathable shoes that aren't keeping your feet too hot. Maybe some cooling foot powder would help.

However, your feet turning really dark is defiantly something that the doctor should see. Take a picture of them when they are like that because they may not look that way when you are at the doctor's office and he needs to see what they look like.

Don't wait too long on this. If they are turning purple or black, you may be in danger of tissue damage if you wait too long. Good luck.