A "charlie Horse" should get better with a bit of massage or gentle stretching. Even a bit of heat can help. If you felt a pop in your calf, have what feels like a knot and continued pain and or difficulty walking, it is possible to tear the muscle. This should be checked by your health care provider should your pain or difficulty continue. Sometimes muscle cramps are helped by tonic water.
The best way to get rid of the pain is prevent it....and its very easy. Eat enough sodium (which is very easy, you probably get enough just from the food you eat already) and potassium, Eat 1 banana per day, bananas have lots of potassium. you will see that you almost never get a charlie horse.
*sodium and potassium are very important for muscles to function properly. When you don't have enough of one of the other, things like a charlie horse can happen.
As for your pain now, lightly stretch the affected leg, every few hours or so, just quick gentle stretch. Take ibuprofen (advil, motrin. etc.) or naproxen (aleve, naprosen etc.) if you can. and just go about your day, it will work itself out
oh, man I hate that...try stretching your leg out and massaging it or go grab a hot bath...that usually helps me.