Open Question: How can I end my life-long constipation?

I'm 18 now and for as long as I can remember, I've always had trouble with bowel movements. When I was about 7 my mom would give me an enema because I wouldn't go, but those would rarely help either. At 13, I had a real bad spell of it. We went to a doctor, he took an X-ray and prescribed some steroids and said if it didn't clear up in 2 weeks, come back. It went away, but ever since then