Bleeding is very common in early pregnancy, especially after intercourse. You can always call your dr for some peace of mind, but generally, as long as you're not experiencing cramping with the bleeding, everything is okay.
There's no general rule as to how long you should bleed for. All pregnancies are different. Some women don't bleed at all & some women bleed throughout the majority of their pregnancies. Good luck to you & congratulations on your pregnancy!