Just want to let you know, that doing FMaths doesn't actually improve your application for medicine, most medical schools don't allow both maths and further maths at A-Level (unless you are doing at least two other subjects as well) since they consider them as one, and some don't even consider them separate at AS-Level (Leicester).
That said, it doesn't make too much of a difference, and I do the same subjects as you might be doing and I hope to apply to medicine, and I love Further Maths. It isn't more difficult than standard maths (at least at AS-Level) it's just more maths, so if you enjoy maths, and quite easily understand it, then take it! Although, only take it if you enjoy it, not to improve your application!