Have a lot of pain from black eye...?!

This is called a Subconjunctival Hemorrhage. These can occur for various reasons. Sometimes people will get them for no reason or because they have coughed, sneezed, or vomited too hard. You can also get them after being punched in the eye. What happens is blood pools in the area of the trauma and you will feel a fullness in the eye. The hemorrhage will get larger for the first 24 hours. If it has not completely cleared up within 2 weeks you need to see an Ophthalmologist. You are probably feeling pain because of where you were hit. When you are hit in the face it can strain the neck muscles and they will be sore for a week or longer! Did you lose consciousness or hit your head on the ground when this happened? If so you may need to be checked for any signs of a concussion or neck injury.
You should see an Ophthalmologist Immediately if you have:
?pain associated with the hemorrhage,
?changes in vision (for example, blurry vision, double vision, difficulty seeing),
?history of a bleeding disorder,
?history of high blood pressure
Since you are having pain I would call an eye doctor tomorrow, explain the situation, and see them as soon as possible. Only call an Ophthalmologist or your family doctor. Opticians cannot treat you for an injury like this.
Until you see the doctor try to rest your eye. You may want to patch the injured eye in order to rest it. Do not drive with an eye patch on. Your depth perception is poor when wearing an eye patch. Do not take any aspirin or NSAID's such as ibuprofen or Aleve unless instructed otherwise by your doctor because they could cause further bleeding in your eye.
I hope this helps.

Nurse for 30 years.

It's because your neck muscles are tight and pressing into the nerves for your eyes when you turn your head. Your neck muscles go to the top of your head, the nerves for your eyes go to the back of your head, passing right next to the neck muscles for this to happen when they get tight. The neck muscles would have tightened up because of the punch to your head as they took on the brunt of the force in trying to keep your head upright. to get rid of he pain you have to free up your neck muscles and here's how to do that:
Neck
Put your hands alongside your head so your thumbs are on the front of the muscle under your ear and your fingers are on the back of the muscle behind your neck. Squeeze your thumb and fingers together and hold. Relax your body. When your fingers and thumb touch, about two minutes, slowly lower your head as far as you can, release the pressure but hold your neck lowered for another 30 seconds.
For best results relax your body first by taking a deep breath and exhaling then remain this relaxed.