First-time pregnant mamas, have any of you dealt with this? I'm at 15 …

First-time pregnant mamas, have any of you dealt with this? I'm at 15 weeks, my belly is still tiny and I sometimes forget that I'm pregnant. I feel so ashamed about it, literally to tears. I haven't had an ultrasound in three weeks and silly thoughts have started creeping into my head — is everything okay with the baby, is the baby where they're supposed to be, is my pregnancy progressing normally?.. How do I fight this obsession? ?