Cryptic pregnancy?

I know medical professionals don't acknowledge this as a real thing that happens, but for the past 4 months I've been suspicious that I may be experiencing this. Has anyone had this happen to them? Or had a pregnancy with hardly any symptoms and not known it? Tests are always negative but researching cryptic pregnancies it sounds exactly what I'm going through! I have a doctors appointment on the 29th because I've missed so many periods, so we'll see what she decides to do. I have been begging her for an US this past 4 months without a period but she refuses unless I test positive. The whole thing is really getting to me. If anyone can share any experience that would be amazing! Thanks