Tucked Vulvia-Infected and bleeding

My dog is 5 years old and  has been dignosed with a tucked vulvia. The vet put her on antibotic (antibiotic) and Estrogen medicine because she thinks she is leaking urine.  My dog has  lost some hair loss on her belly.  But I don't think it is the urine problem.Shehas been on the estrogen medication for weeks and no change.  This problem has been going on since November of 2010!!!!  My dog has never had an accident and I have never seen any urine leakage.  I am with my dog 24/7. I don't see her licking her vulvia but I don't know why it won't heal.  I think it might be an allergy.  She was eating a fish diet but with alpo canned dog food.  The Vet told me to change to purina dog food and I give hert purina one canned dog food with the hard food.  The vet thought the dyes from the food could cause an allergy.  But the hard dog food purina dog chow has diffrent food colorings in it.  It is very diificult to keep changing her food because she is getting loose bowls.  She is snezzing alot.  The vet put her on prednzone and it started to heal until I ran out of the medicine.  The vet won't give me more medicine until I see her again!  I WAS JUST AT THE VET 4 DAYS EARLIER BUT ONLY SAW THE NURSE BECAUSE THE DOCTOR WAS TOO BUSY!  AFTER THE FOUR PILLS WERE GONE THEY TELL ME I NEED TO M AKE ANOTHER APPOINTMENT TO SEE THE DOCTOR IF I WANT MORE PREDNIZONE.  I know that a steroid can help heal it but I want to know what caused this inflamation (inflammation) and bleeding?  Why did my dog get a tucked vulvia at 5 years old? Does anyone what I can do to heal this inflammed vulvia.  She is fixed.  But can a dog that is fixed still go into heat?  If they can go  into heat the heat phase should only last for 3 weeks.  This problem is going on way to long.  Please help me and my dog.  Thank you for reading this and trying to help me!
From, Weezy2011.