I don't think you need to feed it. They grow quite happily on my friend's allotment without ever being fed. You are being too good to it!!

Yes, mine is the same on my allotment, no feeding and light pruning and there is plenty of fruit. I can't stand them though because the seeds are too numerous, get stuck in my teeth and my wife refuses to sift them out. They do make good jelly though,

Pruning correctly is important as they fruit on the junction between the old and new wood and on the old wood. You can safely cut out most of the most recent growth but don't take out the old wood unless it is very old or crossing. The only feed you really need is a dressing of compost or rotted manure in winter if your soil is poor, and a feed of high potash fertiliser around February. If you feed more frequently with a general fertiliser you will get leaf at the expense of flowers.