I don't know how old you are, but I am almost 50 and I find in the last year I have been seeing more back fat too
... I read somewhere that older women tend to accumulate fat back there as they get older
... I can't remember where I read that. I've even noticed that slim older women (older than me) at the gym have back fat too. I am presently working really hard to get rid of it.
On the weeks that I eat extremely clean, drink my water and exercise a lot, the back fat goes down, I just wish I was more consistent.
There is no such thing as spot reduction so I guess we just have to keep trucking with weight training, cardio and clean eating ...