Breastfeeding Woes

I've been having problems breastfeeding since the day I had my baby. After only a few days of breastfeeding my breast were so tender, my nipples were bleeding and sore, and my breasts hurt so much. After a week, I developed a 104f temp and had to go to the emergency room. That's where they told me that I had developed mastitis in both breasts. They were so painful but eventually it went away. Now, six months later, i'm still having problems. I think I have a "overactive letdown" but I haven't been able to speek to my doctor about it. It takes a long time for the breast milk to letdown and when it does it is painful like someone hitting me across my chest. It comes out very rapidly, my baby is gulping it down and frequently gasping for air, and ends up having lots of gas. All of the breastmilk has come out w/in about 3 to 5 minutes. I wonder what i'm doing wrong. What could be causing this problem and what should I do? -mello