Itchy Pooch

Question
My (spayed) border collie mix seems to have seasonal allergies.  She is nearly two and we had problems with itching last summer.  This year she seems to have worse symptoms that started earlier and have lasted longer.  When we took her to the vet, he gave her a cortisone shot and told us to keep her off of carpets and furniture to prevent contact dermatitis.  She is fine in the winter, so I don't see how that could be the problem.  She gets treated with Frontline once a month and gets flea baths in between, but she's not improving (I check for fleas and may see 0-1).  The shots make her incontinent, and I've read they're bad for long term use anyway.  I've tried giving her fish oil once a day, but it didn't do anything.  Is benadryl my best bet?  She's 35 lbs so I know the dose is 25 mg, but is it safe to be used long term?  Is it really effective at preventing vomiting?  She throws up bile and acid in the morning up to 3 times a week.

Answer
Hello I'm not usre if benadryl does anything for vomiting infact I don't think it does. It wont hurt to give it to the dog for life...my dogs have been on it for in the case of my older small dog almost three years and my other small dog has been on and off since she was 8 months old and she is now 1 1/2 years. One  25 ml  pill every 12 to 24 hours depending how itchy she is.