Get an air purifier for in your home and in her room.
Allergies, can occur at ANY time and at any age.
And sure, your child has had a combination of being sick and also having allergies. So that compounds things.
I grew up with allergies and Asthma.
Allergies to dust/pets/pollen and anything in the air.
My parents had air purifiers for our home.
That is a proactive thing to do.
It is an investment, for health.
Even if nothing has changed in the home, allergies can crop up at anytime. Any age.
Even with vacuuming.... it kicks up the air for about 1 hour after. My Doc, told my Mom, to NOT be in the room, while vacuuming is going on, for example. Because, she has allergies.
So that is 1 example.
And if you think the Allegra is not working, then try another brand.
ie: Claritin for kids.
Zyrtec (although I don't like Zyrtec because it makes me moody).
These things affect everyone differently and some works for some and not for others.
Allergies: do not cause fever. Only illness does.
Not all antibiotics may be effective. If one antibiotic does not seem to work, then another family of antibiotics should be used.
But antibiotics does not work, for Viruses.
Sinus Infections can also cause, continual nasal dripping and mucus production.
And, if she goes to daycare or school or something, with other kids, a child often does get sick. And it can be back to back.