First of all, please do not self medicate. Next do not irritate this region any further as all the activities conducted by you (shaving, itching, etc.) have only resulted in further aggravation of your condition.
Next, the cause could be a simple ingrown hair that you have irritated, folliculitis
(inflammation/infection of a hair follicle) or even a sexually transmitted infection (I only assume this as your sexual history is unknown to me).
In such a situation it would be best to visit your doctor and get physically examined. This will have to be followed up by laboratory investigations to confirm your diagnosis and get treated accordingly.
In the meantime, wear comfortable undergarments, avoid sexual contact of all forms, take warm sitz baths several times a day (you could add epsom salt to your baths) and also apply warm compresses to the region with a sterile pad or cloth.
Hope this helps.