Whats the best way to relieve hayfever/allergy symptoms that have persisted over 1 week?

Cetirizine/Zyrtec. Cetirizine (generic of zyrtec) 10 mg, 1 tab, at bedtime is most likely of the otc antihistamines to give relief with minimal, if any sedation. Response is variable so individuals who don't do well with Cetirizine occasionally respond to Loratadine (claritin) or fexofenadine (allegra). If these don't help see allergist who may give an intranasal corticosteroid nasal spray (very effective/safe).
Several. I start with antihistamines. Otc are available. Benadryl, (diphenhydramine) loratadine, zyrtec & others. Next, use nasal steroids sprayed directly into the nasal passages. Other meds such as cromolyn and singulair may help. Though controversial for some, a pulse of oral steroids will rapidly abate the acute attack as will an im injeciton of short acting & long acting steroids. Chime in allergists!