Lump on the back of my neck under piercing?

I have 2 surface piercings on the back of my neck that I've had for 1 1/2 years. The one on the right side often gets pulled or snagged on things so it tends to get sore and red once in a while. It's been acting up for about a week and yesterday, I noticed a lump, about the size of a grape, about an inch below the piercing. It's very painful and my neck is extremely stiff. I went to the hospital today and my blood work was fine, but the doctor wants an ultrasound of my neck. He said he doesn't think it's the piercing because it doesn't look infected, but what could it be? I'm worried and won't get the ultrasound for another week.