Throbbing pain behind neck and in head.

So recently my mom started feeling this throbbing continuous pain behind her neck, around her nape and in the back of her head which slowly increases and the whole head starts hurting. She noticed this pain sometimes when she is looking down or picking something up and then looking up, but sometimes it happens randomly. A year ago, she had an issue where she was sleeping and then when she opened her eyes to look up, everything started spinning, she couldn't lay straight and it was a bit better when she turned sideways, so we went to see a doctor and her blood was quite low 6 but after medication n ol, she got better. Recently also for her frozen shoulders we had some tests and her Vitamin D was around 6. Just giving some background information maybe it can help. The current issue is throbbing pain.