The vinegar test is for warts. Red itchy vagina can be due to a number of causes. First of all it can be due to allergic reaction or contact dermatitis to your undergarments, sanitary napkins or tampons, soaps etc.There is no change in the colour or smell of discharge in this case.
Secondly, It can be due to STD’s but there is a change in the discharge in that case. You need to get a cervical swab and vaginal swab done to confirm the diagnosis.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.