What Are The Symptoms Of Miscarriage?

I am 21 years old. I had sex on July 6th and 7th. My period was supposed to come on July 20, but it did not come one. Instead, it cam three days later [Wednesday], and went off Friday [half day]. It is now August and I am I guess having a period. I am eight weeks pregnant from what I know. I have all the symptoms. I also took 3 home tests and they were negative. I am bleeding does this mean a miscarriage? Is this normal?