What to give my cat-allergic son?

Good evening, my son, soon to be 4 years old, after a visit to my sister's house who has cats and a rabbit, Coco spent the evening sneezing and then his nose became congested. We gave him a dose of claritin for children before bedtime because I think he had an allergic reaction to animals. 1 hour after he went to bed he had a coughing fit like a bark. We took him and made him drink ice water and tried to make him breathe the cold air of the fridge like when he had laryngitis 2-3 weeks ago. 3 weeks ago the doctor we saw for the laryngitis advised the use of advil for its anti inflammatory properties. Should we give it in this situation? And in addition to claritin is it safe? Can an allergy happen so suddenly when it is not a first contact and cause re-inflammation of the larynx?