Where to start....

DS is now 5.5 months old and for the last 6 or so weeks has been slowly getting more and more agitated when feeding. I was on motillium pretty much from the moment i got home from hospital (to increase milk supply) and I just recently weaned off them...about the same time DS has started to get cranky. He's currently feeding every 3 hours or so...the feed starts off normally but within a minute he starts squealing/crying, arching his back, kicking his legs until he breaks off...this happens constantly throughout the feed..i usually give him the dummy in between him breaking off in order to try to calm him down. Its getting to the point where hes frustrated, im frustrated and the feed ends with both of us in tears!! He used to feed 10minutes on each breast...now im lucky if he feeds for 5! He cant possibly be getting enough! The strange thing is that the only time he doesnt cry during a feed is overnight...im putting that down to the fact that hes tired and not sucking so vigorously. I became so frustrated with the whole thing that I caved and bought formula last week and gave him a bottle at about 10.30pm one night and he slept right through! Must admit I felt pretty guilty doing that but i was just at my wits end! Ive spoken to my maternal nurse about it as I thought maybe he had reflux but she doesnt think thats the case...she suggested instead of using the formula to top him up after the night feed with ebm. Thats all fine and dandy but what about this screaming fit he has all day!! I did a trial on him this afternoon...gave him a bottle of formula and he took it no probs...bought tears to my eyes cause it makes me wonder;
Does that mean hes not getting enough from me?
Is he not getting it fast enough so he gets frustrated (preferring the bottle)?
Does he in fact have reflux and therefore take the bottle well as hes feeding upright?

I expressed about an hour after feeding him the bottle and managed to express 100ml (10 min on each boob)... i know bubs are more efficient at feeding than a machine so surely it cant be a supply issue? Have tried expressing first then feeding in order to try to make it easier on him but that didnt work..dont want to go back onto motilium so am going to try some fenugreek and blessed thistle to see if they help but am at a loss as to what else to do! Could it be a teething issue?

Far out this has become an essay (sorry!) but before i go completely insane wondering what the problem could be thought it might be good to turn to you lovely ladies full of wisdom! What am i doing wrong? Dont want to stop breastfeeding him as im really enjoying it...not to mention the goodness it does for him

Any wise words for me??