Last week. I had stiff neck but since then I still have stiffness in my neck and in my shoulders?

Heat & exercises . Without more information, it is not possible to try to determine the cause of your pain. Would recommend trying an otc NSAID along with stretching exercises. If the pain persists then you need to see your pcp.
Mostly just time. For most muscular symptom presentations in the neck, it takes a little time to clear. Sometimes, this may be an initial symptom of another problem like a disc herniation.