It could be floaters. I had some appear suddenly in one eye many years ago. Drove me crazy as I thought there were small bugs flying in front of my face. Still have them, but I've managed to ignore them for the most part.

I notice floaters more in sunny weather or like you, when looking at white or light surfaces. Annoying but harmless. Floaters shouldn't change your actual vision; they're just annoying. I've heard they're more common as we age....

Hopefully that's all it is, but good that you have an appointment - you'll know for sure then.

Carol