With the history of horse riding, it could be more likely that you may have traumatized your perineal area resulting in the swelling. Yet, since it has been there for too long, you should get it treated properly to prevent any further complications. Application of cold
compresses can help to reduce the swelling but unless the specific cause is attended to, complete relief is not possible. Please do not feel embarrassed to ask your mother and get help, since you are quite young. Hope this helps.