I have just seen this as I was working my way back from the Photo board.
With sandy soil, vermiculite is your friend Ria. When you are adding mulch/compost double its volume with vermiculite and dig it in well. It holds water and is a sort of light clay which will help to bind the soil.
Also, if you have an old blender, or can get one from the charity shop, think about making your own liquid compost from vegetable peels, fruit past its best, old tea bags and even egg shells etc - don't use meat, dairy or fats. Bung the things in the blender, just cover with enough water and blitz. If it is a bit thick add more water bit by bit - you do not want an exploding blender! Pour it round the plants then the next day either dig or water it in. If you make a lot it will save in a covered bucket until needed. If you have weeds (dandelions, nettles, dock) you can get your own back on them using this method, but make sure to remove any seed heads before starting.