I am 36 weeks pregnant and i have a rash on my scalp?

i am 36 weeks pregnant and i have a rash on head my doctor suggested that i stop taking my prenatals....it frickin itches so bad its only on my scalp but seems to be spreading behind my ears and to my shoulders,it feels like my skin is raw and little bumps are on my scalp now its been about two weeks now is this an allergic reaction anyone else has had??