Early miscarriage symptoms?!

So this is my second pregnancy. My first pregnancy had no complications, besides a UTI in the beginning of it. But I was wondering what are some symptoms of a miscarriage this early on? I'm 6 weeks today. I'm worried because I haven't had an ultrasound done yet. I won't get one until 12 weeks. I do have some symptoms but nothing really substantial. Like no morning sickness. I might just be a lucky one. But is it possible to miscarry and without having substantial symptoms?