Hi Robyn,
Yes both ivy and lilies could be the cause of contact dermatitis and it is possible for the rash to be more widespread that at the actual point of contact. I do wonder at the duration unless there has been ongoing exposure to the plants. There are plenty of other possibilities for gardeners, including cleavers (sticky weed) and rubber gloves, and the cause may be quite tricky to sort out. If you feel you are not winning I suggest you see your GP or a skin specialist. Having said all that I agree that Astrid's suggestion would make a good start.