I had exactly the same and also on the R side, happy.
It always helped me to get DD on the R side during her sleepier feeds first and massage, massage, massage.
It was only after she weaned and during an ultrasound for lumps that never went away that I found out my milk ducts on the R side are very twisted and contorted compared to left so DD being a very impatient little soul was not patient enough to wait for the letdown from the twisted ducts (DS was similar but much, much older when it happened) and so fed less from this side or less happily anyway. I would usually start with R side for first morning feeds if I got to her when she was only fussing a tiny bit, same for middle of night feeds and DFs and for the more ravenous and awake feeds I would trick her by starting in trad position on the left and then moving her when I got the letdown going (thro massage) on the right and moving her there in a football hold in one foul swoop IYKWIM?
Of course, with such a great weight gain, you may be better off teaching your right side to produce less and less - best way for this is through ice packs after a feed and pumping only when necessary from this side. I fed mainly from the left side for the last 4-6 months of feeding both of mine - was a little lopsided but at 1yr plus I couldn't trick them into feeding from the R side anymore...
S x