Is this a miscarriage? (details, don't read if you have a weak stomach)?

I'm sorry to say that yes that was a miscarriage in the very early stages of pregnancy. That much blood with cramps of any kind during pregnancy is a sign of miscarriage, and the fact that you got your period now would tell you that pregnancy has been terminated. The two negative tests could just mean that you tested to early or that there is not enough hcg in your urine yet. Sorry and good luck in the future.