It is hard to sustain a store with only a few items listed, works much better if you use all your free listing allowance. Also why not try listing a few related products so you are more likely to appear in searches and people may buy one of your prints with another item.

Times are hard and more and more people are going to look at cheaper ways of doing things, if I wanted something like you are selling I would create and print it myself.

You may have had a niche market for a while but others looking to start selling on ebay may have seen your products, realised they can do similar and so started selling in competition. To succeed long term on ebay you have to be prepared to be flexible and to change your business model if needed.