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That's not much information to go on for a remote diagnosis. We would need photos, your location (what's Sw5?), the type of camelia and age, previous history of growth and blooming, and more about your soil fertility and water managment. Any recent disturbance of soil nearby, root cutting, compaction or paving, undergound water or gas leak?

Without background information, I can only recommend to consider mulching, fertilization and good water management.

Did they come in those pots, or did they get re-planted? This usually happens when there is too much nitrogen available in the soil. You may want to halt feeding for quite awhile, or if you used a very nutrient rich soil or compost, then you may want to use a lighter soil.

This article will give you more information: https://www.gardeningknowhow.com/ornamental/flowers/camellia/camellia-fertilizer-info.htm

This could, actually, be many things. There are some things that you can do for a general pest infestation. This link will take you to a collection of articles that will help you to make your own pesticides, plus much more information: https://www.gardeningknowhow.com/special/organic/

Multi-purpose is likely to be slightly acidic due to the peat moss. Does the bag give the pH of the contents? If not, look on the companies website. There are several products, like slow-release sulfur, that lower pH but you won't know how much to use without first knowing the present pH. You might also use a fertilizer designed for acid-loving plants. It is intended to lower pH and feed plants being grown in neutral to alkaline soil. The following article discusses lowering pH. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/raise-acid-level-soil.htm

In your area it should self seed, however, those seeds will take years to flower. This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/flowers/camellia/caring-for-camellias.htm

Sure, I have just the article for you: https://www.gardeningknowhow.com/ornamental/flowers/camellia/pruning-camellias-how-to-prune-a-camellia-plant.htm