Thanks for the info, Beastly.
I don't think there is a feeding problem to fix.
I don't think getting more out with expressing, using a different pump, switching to expressed, or switching to formula will help in any way at all. His behaviour has nothing to do with working out that the bottle is easier because a) it isn't easier and b) 20 week old babies don;t have the congnitive skills to draw these conclusions.
This is a baby of 20 weeks old - unless you tell me in your next post that he has had long-standing difficulties gaining weight, and he is now, at almost 5 mths old, skinny and miserable because he is not getting enough to eat (and I don't think you will), then we can look at his behaviour rather than his nutrition.
At this age, babies take much less time at the breast. They are done in a few minutes. If their mothers insist on putting them back on again, they will object - they may bob on again and then come off and behave restlessly and seem unhappy.....because they are unable to communicate in a way that gets what they want.
It is highly relevant you are stress and unhappy in other parts of your life. This has a number of effects: for a start, it leads you to micro-examine your baby's reactions and behaviours and interpret them in a way that leads you to think you are failing somehow; this doesn't help, and it makes you more stressed and anxious, which makes the issue worse; your stress distances you from your baby, and he picks up on this, not in a cognitive way, but in a feelings way, and this affects his behaviour.
Finding ways of dealing with the stress and anxiety without the panicky responses you say you are experiencing will help - but you won't get that help by thinking it's a feeding problem, I don't think.
Getting help will mean you and your baby can tune into each other better and this will mean feeding does not add to your stress.
Have you got a good HV you can talk to, about your stress, your unhappiness and the lack of confidence you feel?
I hope some of this strikes a chord with you.