Give it time, obviously. However, hill repeats will help to build strength. Consider some plyometrics, as well. Stretching won't help a great deal if the strength isn't there. Don't forget a good warmup before a workout, then stretch afterward. I find that if I do a lot of treadmill running (winter) when I hit the streets again my calves hurt no matter what. However, a week or two into the spring and they feel fine. You'll build up to it.