welcome to GoY.
the yellowing leaves is usually a sign that it needs to be in acidic soil/compost. You should be able to get a plant feed specifically for camellias/rhododendrons and that will help.
the curling leaf could be due to lack of water.

Check underneath for any sap sucking insects such as scale insects and aphids.

Sydney, Australia? Frost shouldn't be much of a problem, there. On the other hand, the soil will be pretty poor, and it may be necessary to put in a handful or two of cottonseed meal (if available) and the same of kelp meal. Soluble fertilizers for acid loving plants will be faster-acting, but will make the soil worse over time.