Is a little blood common?

I just found out I'm pregnant by using a hpt a few days ago. So I'm about 3 weeks. Today while using the bathroom i noticed there was a little bit of blood in the toilet and i freaked out. Looked like just a few drops of bright red. If i wasn't pregnant this would be the time I get AF. I don't have my confirmation of pregnancy until tomorrow morning. So far i have used the bathroom again and there's no more blood. Is this normal or cause for concern?