(since he doesn't seem to get enough in one go, I think he is lazy and gives up, knowing mummy will get him the easy bottle!)
He's too little to be thinking this way. This might just be how he rolls. My baby is a snack feeder, and even at 8 months, likes to feed hourly, although now it's only for 4 minutes at a time.

I second the recommendation to see a Lactation Consultant. A mum in my play group was doing top-ups from 3 to 6 weeks, but by 3 months her son was exclusively breastfed, because of the help that she got.