I think this is due to frost damage. Camelias need protecting through the winter months.

without a photograph, I would suggest that the yellowing leaves are a result of mineral deficiency from not being in an acidic soil.
The immediate fix is to feed with a specialist camelia liquid feed (exactly as the instructions on the bottle) or a slow- release granular feed now and again in June/July.
Longer term you may need to consider transplanting your camellia into a pot with ericaceous compost.

Do you know the variety of Camellia? Also how old is it (a well established plant or young/newly-planted) and what sort of soil is it in?

Hi, welcome to GoY, I agree with Urbanite, if you haven't got acidic soil, it would be better off in a large container with ericaceous compost.
Don't worry about hardiness, there are over 250 species of Camellia, and very few of them are not completely hardy, the more tender species are less likely to be easily available, the most common species, C japonica, is completely hardy, but don't plant in a position where it will get early morning sun, especially after a frost, as this causes the buds or flowers to drop, Derek.