Well, if I learned anything from the movie "Dirty Dancing" it is that you walk on your toes, not on the heels. This means you need some serious calf muscles to pull it off, which is why women who wear heels all the time don't have a problem with it, they've built all the correct muscles already. This is also why it's painful and a hassle to learn to wear heels.
Do calf exercises, stand on the bottom step of a flight of stairs balance with the front half of your feet on the steps and your heels hanging off. Use your calf muscles to sort of bounce up and down.
Or just walk around on your toes when you're wearing other shoes, this will build the muscles too.
You'll be walking comfortably in heels in no time.