What is wrong with me?

Staying bubbly especially when you have some anxiety is hard work. Don't be hard on yourself and expect to be perpetually positive. It's normal to feel tired through treatment, tired of it and tired by it, even occasionally despondent. I'll bet you don't give any indication of any worries to those around you, especially your family. Allowing yourself an occasional wail, perhaps in private, is not only allowed, it's possibly good for you. Doing it here is a good option, we've all been through it. It helps you return to being positive once you vent the negative. Pre- test anxiety is so common as to be practically mandatory, you will almost certainly feel much better after the 13th. Best wishes.