Baby seasonal allergies ftm

Hey ladies, ftm here. I have a 8 month old baby girl! She has had a nasty cough for about three weeks we have been to the pedi. Twice and he says is just seasonal allergies and to give her a nasal spray and Benadryl. Sweet baby girl just sounds horrible and the cough isn’t any better. No fever lungs are clear. Any advice how to kick this? Texas isn’t very allergy friendly I get that. Thanks in advance.