Leg pains

So every since I was little I had leg pains. Doctor used to tell my mom that they were growing pains. Now I'm 25 and still have them. I walk 5 to 8 miles a day at my job...but have been doing this for 5 years now. Shouldn't my body be used to it? I'm at a loss. Sometimes it's so bad I could crawl up in a ball and cry. Anyone else experience this? Anyone have any suggestions?