Vitamin D is the first supplement I would suggest for allergies. Unless you live where there is an abundant amount of sunshine and can be outside daily, chances are your vitamin D levels are low. Vitamin D deficiency is widespread even in areas where there is plenty of sunshine.
Simply taking some vitamin D could improve your allergies within a few weeks. It may take longer if your level of vitamin D is low. While waiting for vitamin D levels to rise look into quercetin and bromelain for some faster relief.