Well the average age for menopause as far as I am aware, is approx 51 years of age, so it would be an early menopause for you if this is what it is.
If you have been undergoing treatment for infertility, this can play havoc with one's hormones AND cycles, making you think you are pregnant when you aren't and not pregnant when you are!
It's impossible to say, so I am pleased you are going to see the MD and I would go ASAP. If he cannot detect anything on scan, ask him to give you some blood tests to check for early menopausal symptoms and/or pregnancy anyway to be absolutely sure. Most likely, he will do so anyway.