Hello, welcome, nice to 'meet' you,
Firstly this is totally NORMAL, it drives you mad, but when they are so little, it's what they do! Charlie did this for ages.
Secondly, are you using the EASY routine yet (I know your lo's only tiny, so no pressure). The reason I ask is that Charlie only stopped doing this when we started on the routine. He was falling asleep on my breast b/c, bless him, he was tired. As soon as he started having proper naps in the day, and sleeping better at night, he was less tired at feeding time, and the sleepy sucking stopped.
Also, the feeds become shorter b/c he was awake for them & therefore more efficient!
Please don't worry, it sounds like you're doing fine. Your baby is still only tiny and (you're both) learning these things from scratch, it does get better. Keep on this site, there's loads of advice here, and, if you haven't already, get hold of Tracy's book, I think she deals with this subject in there.
HTH!
Caroline