I planted this camilia in my garden and leaves started becoming yellow

Your soil is probably alkaline which Camellia's do not like. The pot you have it in is far too small. Find a much larger pot and use ericaceous compost.

Thank you Moon,yes I have alkaline soil (very sticky hard clay)but I put ericaceous compost in the soil before planting.I will put in big pot soon.I have just put it 2 days ago.

I agree, it needs ericaceous soil and feed. Iron is quite soluble so the heavy rain has leached it from the soil. The new leaves will come back fine after you do that.

Thank you Kildermorie

That is interesting because I have the same problem.