Itchy scalp with no visible signs of disease 18 months after facelift, what could be the cause?

I had a full facelift, with brow lift and neck lift in May 2017. After four months, my scalp began itching, especially at the crown. I lost a lot of hair at my crown, rather than along the scars. My surgeon gave me some Botox injections to relieve the itch at 6 months. I also went to a dermatologist who injected some anti-inflammatory meds in my scalp and prescribed some special shampoo. The hair I had lost at the crown all grew back. It is now November of 2018 and my scalp itches all over now, every day.