I have an 8 year old Labrador Retriever. She is not spayed and is having a bloody vaginal discharge that is very heavy. I thought it may have be a urinary tract infection. I have been treating her with 250 mg of Tylosin twice a day for the last 14 days. She showed some improvement with lighter discharges, but in the last few days it is heavy again. Any suggestions as to the net course of action to take.