Hi Debs, that back taste you are talking about might be tannin, or it could be ALCOHOL!!!
If it is tannin, too much will give the wine that 'stick-to-the-teeth' effect, too little and the wine will be 'thin' or lacking a bit of body. You can add tannin by making a strong cuppa tea, without the milk and sugar, and mixing it into a wine. To reduce it you need to remove skins and seed and stems from any fruit you use before starting fermentation. It is more noticeable in red wines.
If all your wines are tasting the same it is probably because you are not using enough fruit. All the fruit sugars are being turned into alcohol and alcohol tastes of.... alcohol. Either start with more fruit or add some ordinary white sugar so that some of the fruit sugars are left to help flavour the wine.
A few good freebies are coming up: Oak leaf, made from the new leaves; Beech sap, but only one drip per tree; and the Elderflower that you already make.