Having a miscarriage ?

Hello.
i'm 18 years old and not sure if i'm having a miscarraige? i've genuinely thought i was pregnant for the last 5 weeks, i've had all the symptoms, sore breats, more noticeable bumps around my nipples, nausea, dizziness, you name it! i took a pregnancy test which came back negetive, i felt pregnant so i was sure i had just taken it too early. i've come on a week late, but this period is like none i've had before, i've never noticed any clots but they seem to be just pouring out of me. i'm unbelievably heavy and have sharp pains in my lower abdomen. if i don't even know if i was pregnant how can i tell if i've had a miscarriage? will the doctor be able to tell even if i've passed the baby? i really don't know what to do, i'm so scared and really could do with some advice?