Diagnosis of hay fever
Against which grasses, pollen or other substances you are allergic, which triggers so the hay fever, can reliably get out only the doctor with an allergy test. But before he does that, he will try to filter out potential allergy triggers.
If the symptoms of hay fever, especially in confined areas, clearly speaks against pollens or grasses as a trigger. More likely then is an allergy, e.g. against animal hair (are animals at home?) or house dust mites.