Sounds familiar-I demand fed my boy and he did the same thing. I saw a plunket nurse who told me to keep putting him on the breast over an hour, as many times as I can, then put him to bed for a sleep, and start again 2 1/2 or 3 hours after the start of the feed-but he was not interested in that! Eventually, like at about 14 weeks, he started to do it all by himself.
Have you read The Baby Whisperer? She might have some helpful ideas for you.
Breastfeeding is so hard-I thought it would be so natural and easy but it wasn't! You are doing the best thing for your baby-good on you