I'm 15 weeks pregnant tomorrow, and was just wondering what everyone can feel (from the outside)?

I'm not showing yet, but I can feel what I'm assuming is my uterus just above my pubic bone - it feels hard there where it used to feel soft. However, then I reach all my excess stomach fat and can't feel any further up. From what I've read my uterus should be a bit higher by now, but I can't feel it. Of course, this leads me to worry (a lot) that things aren't progressing the way they should be... and my next appointment isn't for another two weeks!

Does anyone know if I have any reason to worry?