What am I doing wrong?

[TheHollyandtheBarnpot]

I have been breast feeding my 15 week old who only properly feeds when he's asleep.
when he's awake his feed cycle goes something like this.
-cry, latches on, feeds for 30 secs
-pushes himself/arches back to come off breast, while still sucking
-cries latches back on feeds for 30 secs
he does this for about 5 mins when he starts smiling and cooing at me and won't take anymore.
things i've tried
-changing his posision ie tummy to mummy, on a cusion, lying down etc
-sitting in a quiet room
-holding him on, he cried even more

I'm really stumped as to what to try next any suggestions?

How long has he been doing this? Or has he always been like this?

hes always been like this, occationally we get the odd feed when he will do it properly and feeds for about 15 mins, but then throws it back at me

Is there anything here that helps?
www.kellymom.com/bf/concerns/baby/fussy-while-nursing.html

thanks grendle, the fast let down sound familiar, he does have all the symptoms, ie gagging coughing, all the while I'm dripping away, will try some of the suggestions.