Red face itching from high hematocrit?

I have thick blood already, last couple months my H may be getting high but cant do blood yet

Ive had red flushing like sunburn from neck to scalp, itching like crazy.

Benadryl takes it away, could this just be high H or would Benadryl not make it feel better?

Going to alergist now.

Doing more blood work in couple weeks.