One drop of blood while pregnant?

I was 7 weeks pregnant, and after using the bathroom I wiped off a very tiny bit of blood. I just wanted to know what does that mean? I am 9 weeks now , but last doctor appointment was at 6 weeks and 2 days and we actually saw the heart beat at that point. However I am currently having a problem with my insurance and couldn't see my doc for 3 weeks. So I am finally able to see the doc next week but Im very nervous and worried over that tiny drop of blood at 7 weeks. I am terrified that when I go to the doc he might say I miscarried . I didnt have any pain associated with the drop of blood and when I went 1 hr later to check I didnt see any blood..NEVER happened again sice that day. I still am tired, sore bigger boobs, morning sickness etc ..I am 24 years old and this is my first pregnancy. Please let me know what you think ...Thank you sooo much