My Dog Is 9 Years Old And Her Breathing Seems More Faster Than Normal, Is Something Wrong?

My dog, Penny, makes 9 years old tomorrow and for awhile now I noticed her breathing to be more faster and harder, like as if she's panting after playing fetch. I notice her breathing to be this way even when she hasn't done any rigorous activity all day. She has had a history of cancerous tumors, which have been removed, and she is also highly allergic and is taking Claritin, daily, for it. Should I be concerned with this new pattern of respiration or is it cause of her age? Please help.