Hello, I Had Full Thyroidectomy On Feb 18 2015, My

Hello, I had full thyroidectomy on feb 18 2015, my allergies are awful iam on 175 levothyroxine and not stable yet as still trying to get parathyroids working, can I take any antihistamine, I tried reactine and it made me almost faint from racing heart, ringing in ears etc, ty so much.