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 like Chlamydia or thrush or thirdly due to lichen sclerosis. It is very difficult to pinpoint one diagnosis without clinical examination and cervix swabs or blood tests. So I feel that you should consult your gynecologist for a complete evaluation as treatment will depend on the diagnosis. Till that time you can take some oral antihistaminics to relieve the itching.
I hope it helps. Take care and please do keep me posted in case you have any additional doubts. Kind regards.