If this very frequent yes he could have allergic problem. Usually in some seasons like winter, rain etc, allergic cases increases due to changes in weather.Occasionaly viral infection can lead to this. Try to vacuum his pillow, his blanket and bed sheet regularly, this are most common source many allergens.Remove any thing which has peculiar smell like mosquito repellents this can help. And in routine give healthy food like green vegetables and fruits which can boost his immunity.