It's too late now, since your appt. is tomorrow, but next time you can start a steroid nasal spray about a week before you stop the antihistamine (these sprays can actually accompany antihistamines and sometimes replace them. They are better, in my opinion because the med stays local in your nose). You can also start Singulair the day that you stop the antihistamine. Neither of these drugs will bother the test. My children did this every time that they had allergy tests.