Congestion may be a side effect of allergies -- a histamine reaction -- so an antihistamine alone may help. Give it a try for a few days first.

Sometimes allergies provoke swelling of the mucous membranes beyond what a safe antihistamine can help. Zyrtec, Claritin and generics are currently the safest antihistamines. If you still experience painful sinus congestion then pseudoephedrine or ephedrine may be the best over the counter remedies.

Keep in mind that both ephedrine and pseudoephedrine can aggravate other medical conditions, especially high blood pressure and thyroid disease (I have both). They're also stimulants, roughly comparable to a couple of cups of coffee. So use them with caution. I use those decongestants only when the pressure causes painful sinus headaches, dizziness, nausea, etc. I wake up with those symptoms every day but often just drinking a few cups of coffee or hot tea relieves some congestion.