Is bright blood and menstrual cramping always an impending miscarriage?

I'm uming I am about 5 weeks pregnant. I just found out a week ago and haven't even made it to my first prenatal yet. Right after I found out, I began having some brown spotting. Just today, I had some bright red on the toilet tissue and I've been having menstrual cramps. I still have the nausea and fatigue. Does this mean I'm going to have a miscarriage or can it mean something else?