What Causes Bruises On The Head?

HI, for the past two days i have been finding bumps and bruises on the left side of my head. one bumo is right above my left ear and another is down behind the back of my left ear. I also have one around the base of my skull and another not all the way to the middle of my head , more towards the left side. The wholeleft side of my head is sore to touch, and I start to get sharp pains every so often. There is also a tender spot on the left wear my jaw starts. I know i didn t hit my head at any point but i don t know where this came from. It just popped up out of no where