A sudden swelling after an insect bite is normal. Kindly look for pain/swelling in throat, tongue and surrounding area. Also look for any abnormal skin patches too, if there . Keep a check of your breathing and heart rate. Applying ice pack is a good step, so continue doing that.
Next Steps
Allegra is good to go for now. if pain develops pair it with an analgesic (painkiller) too. But if the swelling does not subside after 1 to 2 days, ,kindly consult here asap.
Health Tips
Avoid touching, scratching the area.