If seasonal allergies are preventing you from breathing through your nose, you can take decongestants, but they'll end up drying you up everywhere, even your lady business. Plus they can make you feel kind of spaced out and tired.
A natural alternative I've found that relieves congestion is to raise your body temperature through exercise. Choose heart-pumping activities such as running, biking, hiking, cardio kickboxing, or exercise in a heated room such as Bikram or Ashtanga yoga. Do it for at least 20 minutes, and once you start sweating, your nasal congestion will start to thin out a little, making it easier to blow your nose and clear your sinuses. Just make sure you have a pack of tissues with you so you can get rid of the mucus instead of sniffing it back in.
If the pollen count is really high outside, do your cardio inside to avoid aggravating your symptoms.