I've been dealing with the same thing! I got my moderna booster on Dec 30 and my scalp/neck started itching on Jan 9. Then some hives started appearing on different parts of my upper body. I started taking antihistamines (reactine) and it's really helping, but my skin is still super sensitive and red marks appear with the smallest scratch. No throat or digestive issues though.
With antihistamines it's manageable but I worry it will last a long time.
I have not seen a doctor because from what I read online there's not a lot that can be done.
Has it been getting better for any of you?