I am having huge trouble with my 3 month of ful...

I am having huge trouble with my 3 month of fully breast fed baby. He has got to the stage where is he is completely refusing the right breast. I always offer the right side first and he just screams as soon as I lay him down on the side. Sometimes he will take a few sucks then start screaming, but most of the time it is as soon as he is in that position to feed. I have tried repositioning myself - sitting in different chairs, no pillow, with a pillow, lying down feeding etc and nothing makes a difference. At first I thought it could be that the flow was too strong on that side as this was suggested to me early on. The side that he refuses always made a lot more milk - I successfully breastfed his sister for 9 months with it & I had to express for the first two weeks of his life as he was in NICU and that side made way more milk than the left. I really don't know what to do and it is starting to stress me out big time. Is he getting enough milk just off one side?? In the last 24 hours he has probably only drank off it for a total of two minutes and this is a typical days example. Sometimes I have to express off it for comfort, other times (like last night) I just leaked a lot out of that side overnight. Also can one breast supply enough for a baby? Once he has finished feeding he always seems satisfied. He will go 2 - 4 hours between feeds during the day and generally has a 7 hour gap overnight. Any advise would be appreciated as I really want to exclusively breastfeed him as long as possible as he had another health issue unrelated. Thanks for reading if you have got this far - sorry I know it is a long one!