I have same problem and used nipple shields for a few feeds - I think it helped a bit, but then I worried about it affecting lo's latch (she tended to nipple suck, rather than do wide open mouth on the shields), so I stopped.
I did find that pumping a fair bit (for 5ish mins, getting off about 50 ml milk) first helped - but that's such a faff and often involved letting her scream head off while I did it, which wasn't fun for either of us.
It has settled down for me a bit now (mine is also 7 wks), perhaps my supply and her demand is finally beginning to get in synch? Or she's getting better at coping with my oversupply? Mine also had tongue tie and once that was snipped, she seemed to be able to cope better (although the posterior tt grew back and one of the reasons I suspected that was because she'd become fussy again and seemed less able to cope on my oversupply side).
Oh - also, make sure you burp him frequently, because all that coughing and spluttering will give him wind, which makes the fussiness worse. When it is/ was really bad I would wind mine every time she spluttered off and that seemed to help.
I feel for you though because I know how miserable this can be - nothing worse than trying to feed your lo and him/her seeming to get so upset at the breast. I went to multiple bf drop-ins to get help with this and the upshot of the advice was you just have to persevere. They also suggested leaning back to feed/ feeding in the 'laid back' or 'biological nurturing' position although that never really helped us.