My period came like normal, and lasted only three days, but it wasn't like normal. The first day was really heavy and dark, second day was really light and like it wasn't their, and the third day it was really dark and spotting. Could I possibly be pregnant?

Sounds to me like you just had a period. Given that it seemed to have arrive on time, it may just be slightly irregular this month. However, if you are still concerned, wait a week and take a HPT. Most of the time, though, it is the lack of bleeding that is the telltale sign of pregnancy. Good luck.