Duration of facial swelling for dogs with bee stings?

My dog has been bitten/stung by either a wasp, bee or spider (aren't sure which) on three separate occasions and I've self-administered Benadryl on two of those occasions. The first time, I took the dog to the vet. On that occasion, they gave her an injection of cortisone and Benadryl. The effects took place rather quickly - within minutes the swelling went down and the dog looked fairly back-to-normal within a day. On the two occasions that I self-administered just the Benadryl (orally, and did not give cortisone), it took about three days for the dog to look "normal" again, but the effects of the oral Benadryl were noticable after about thirty minutes (i.e.: the swelling began to go down about thirty minutes after I administered the drug.). I felt it was okay to self-administer because other than the facial swelling, the dog was acting normally, had a normal appetite and normal energy level. She was also able to swallow and drink normally. If your pet is not able to do any of these things, take him/her to the emergency/vet immediately! I hope you find this information helpful.