The only thing I can say is that every pregnancy is different, some people struggle with sickness and fatigue for a lot longer than others.
I know Im a few weeks behind you, but i barely have a bump and I can fit into most of my work clothes now. But again, everyone is different. Just depends on how you were designed! A lady I work with was pregnant and didnt begin to show until 30 weeks, and when she was full term she still looked tiny, but had a perfectly healthy baby at 8lbs. So I dont think you need to worry about that either.
To be honest, I feel like you a lot of the time. We hadn't been trying for our baby, it just happened and even though Ive seen it twice now on scans, I still don't feel like its real most of the time. I dont think it will sink in until Im holding it for the first time.
I think a lot of the things you've said are quite common... or at least thats the way Ive felt! But Ive found comparing yourself size-wise and symptom-wise wont do you any good, because everyone is so different!
I hope you start to feel a bit better soon

Your midwife might be able to reassure you further
xxx