Miscarriage/ Unviable pregnancies

I hope this doesn't rub anyone the wrong way or bring back traumatic memories...
If you've ever had a miscarriage how did it start for you? Did you know you were miscarrying? What were your symptoms? And if you've ever had a blighted ovum or unviable pregnancy, did you know from the beginning that something wasn't right? What were your symptoms of that? Thank you in advance and I am so sorry for your loss. 
I am asking this because I've had a feeling my pregnancy isn't viable and I am really worried. It's my first pregnancy and I haven't had my first ultrasound yet but I am terrified to go- I feel like there isn't going to be anything there 😢 I check for blood every time I use the restroom.