8 weeks pregnant and bleeding

I am 8 weeks pregnant and had sex with my husband sundy night, when we finished we noticed that i had started bleeding. it was nothing heavy, it started out a slight pink with red and then has turned to a dull brown with red. i am not filling up a pad at all and when i do look at my pad it is light brown, i am not having bad cramps and i called the doctor and they said this is normal. my thing is how long should the bleeding last for and is this really normal or should i worry. i dont feel the normal pregnany symptoms, like sickness or breast tenderness anymore