How long have you had it, and is it in a pot or in the ground?

You've told me its 7 years old, and is in the ground, and that you've just joined, so welcome to GoY first!
A photograph would be really useful, but if that's too difficult, inspect the plant all over - the backs of leaves, stems and branches. You're looking for insects, funny deposits, black or discoloured areas, anything that shouldn't be there. I just want to make sure it hasn't got scale insect infestation which, on Camellia, is more likely to be present on the backs of leaves.
Assuming you find nothing, and that the ground its growing in is normal, garden soil and not a small enclosed space, feed with a general purpose fertiliser such as Growmore or Vitax Q4, raking it in around the base, or with a soluble plant food such as Miracle Gro general purpose mixed in water, and then water on a solution of Sequestrene iron tonic, comes in sachets in a box from the garden centre or Wilkinsons.