
Ideally you should see a doctor or gynaecologist, but as you say this is impossible we can only give guesses as to what your problem may be.
Are you sexually active? if so it could be a reaction to condoms, a reaction to vigorous sex, a reaction to lubricant or anything else you may be using. Although you say there is no discharge it could be an STI. Can you get to an STI clinic?
It may also be a blocked gland..possibly a Bartholins gland, which may also be infected, and your labia are also reacting.. Can you bear to sit in a warm bath or apply warm flannels to the area? Do you use any sort of perfumed lotions or soap or shower gels on that area? If so do stop and use only a bland soap, and very briefly . Dont use any of the feminine washes, they can cause irritation. Dont wear thong pants or any nylon or polyester pants. Wear only cotton . If this is painful then take Ibuprofen but no more than 6 per day.
I see you are 18…do you have a Mum you can ask about this or sister or close friend you can take into your confidence.
I am guessing you are not in UK as you have mentioned that you cant afford treatment. If you are in UK then do seek help from your doctor.