Good night , you probably just hurted yourself, did someone or something hit you in your private area ? If not , you could have gone too hard on mastubation and ended up hurting yourself without even realising that. If it doesn't hurt , it might not be anything serious. Wait a a little bit longer ,try not to masturbate ( or dont go so hard) and wait a week or so , see if it gets better , if not you better see a doctor to see of there is no problem