As I said, you can't be pregnant if you don't have sex - additionally you are on the Pill. I can't say why your doctor said what he/she said.
Additionally, the body doesn't work like clockwork - irregular bleeding can happen, even while on the pill.
Take a test - that is the one way you will know. There is no point in wondering and worrying about it if there is a test that can tell you within a couple of minutes.