Pain in my calves, but wanna keep running!

[Scrap]

Stop running down the hill to much impact

[Chris Nagel]

Impact, lack of preparation (warm up and stretching), and bad posture or running technique (shoes can also affect this) is likely to be the problem is.

Try to cut back on your running until your shins recuperate, perhaps give it a week and then see how you're feeling. Stretch your legs regularly, especially your calves, and it would also be a good idea to check out some books on running technique in the meantime. You can do some form of zero impact cardio to keep active.

When you start running again, pick somewhere else to run besides on concrete if it's possible. Cross-country is nice, a horse track is even better, and even a school/college track is better than running on concrete.

For about 10-15 mins run at an easy pace to get warmed up, then do some dynamic stretches for about 5 minutes before you're actual run. While your running concentrate on your breathing and technique more than trying to beat your last time.

You could get a heart rate monitor, they come in different forms now, I think the watch and belt kind is the most convenient. The heart rate monitor can help you set your pace/intensity accordingly and when to have a rest interval. Interval running is easier on your legs than a long hard run any day.

[AdamGB]

Like Scrap says go easy down hill, your calfs are trying to contract/stretch at the same time: Could cause problems.

Do you stretch before you run? Personally I wouldn't... if you have to then just do a light stretch only holding 8-10 seconds even then make sure to warm the muscles with some slow jogging/quick walking first.

Stretching can cause microtears in the muscles/tendons if you haven't warmed up properly... you need blood pumping to the muscles and for them to be subtle from the warm up before you stretch... or else you get these tears and then when you go on to train the tears become bigger and you'll have over-damaged the muscle.

I don't stretch before a run, I brisk walk into a light jog and up the pace from there.

[Scrap]

Never before, always after. Nice one Adam good tip

[Howlin Mad Missy]

Adam & Scrap are right, no need to stretch before a run. If it were your upper body you could include some ranges motion/mobility exercises but for your calves all you've pretty much got is to point and flex your foot.
Walk, jog, run. Stretch out after you're warm.