My Skin Is Itchy Me Prickly All Over My Body.

My skin is itchy me prickly all over my body. There is no rash and Benadryl relieves itchiness to some degree but not completely. I've been on synthroid for 3 months, 2 months with 50 mg. which did not get thyroid working properly, and now 100 mg. I've had this symptom for about 2 yrs. which is about the time I believe my thyroid stopped working properly. Could it be related?