Could i be pregnant?

ok i had my periods 3 weeks ago,and i had unprotected the week after....but for the last few days i have been felling very tired and like i am going to get sick all the time?. . .this morning when i woke up i wnet to the toilet and the was a little bit of blood! i shouldnt get my periods untill next week and they are always regular. . and very heavy!..but it was only a little bit? could i be pregnant?....please answer?..tanx..xx