English Ivy generally prefers semi-shade to shade areas. It also needs quite light soil as it likes to be aerated and not have wet feet.
You may have it in too much sun, or perhaps may be overwatering it. What type of soil do you have it in? Is the soil staying wet? If so, you are giving it too much water.
I am not sure how hot it is where you are, but full sun may just be too hot for it.
VAL (Grandpa's Rose)