I personally would be skeptical that your son is experiencing seasonal allergies. Many pollens are on a perennial schedule and being that he is less than a year old, he likely hasn't been exposed to these pollens before---the first exposure is usually not the time allergies present, but the second time and thereafter. It's not impossible----but I would consider other causes such as a recent food addition or more consistent allergens in his home environment such as dust mites or pet dander. I would also think you can't rule out a viral cause. I would also agree with the symptomatic treatment suggestions already offered.