A significant amount of swelling can occur after an insect bite/sting and may continue to increase for several hours before gradually settling. The fact that you have no pain, irritation or other symptoms is reassuring.
Next Steps
For now, continue cold compresses/ice wrapped in a cloth for 15–20 minutes at a time, with breaks in between. Since you have already taken Allegra, don't take additional antihistamines unless advised by a doctor.
If the swelling is very large or continues to worsen despite the antihistamine, it would be sensible to get examined today rather than treating it only at home.
Health Tips
If the swelling starts involving the tongue, inside of the mouth or throat, or you develop difficulty breathing/swallowing, throat tightness, wheezing, dizziness or widespread hives, seek emergency medical care immediately. These can indicate a serious allergic reaction.