May be time to pull the plug on it and try something else. Some varieties perform better than others ~ and some just don't to much at all. Out of about 20 varieties I've tried over the years, maybe 6 have been worth keeping. The weak producers have a good year now and then so I keep them around. You might want to try moving it to a different location for a year or two as the spot you have it in now may not be conducive to good growth for one reason or another. Do a trade with someone for something different and you may be surprised!
"Neil & I would've tweeted from the moon if we could have but I would prefer to tweet from Mars. Maybe by 2040" ~ @TheRealBuzz, Buzz Aldrin 11:20 PM - 04 Jan 13