Could I have a concussion?

Today at this camp counsellor training (I'm quitting this crap), I was sitting down in a Circe for a game that involved running. Someone was running very fast and his knee hit my head very hard. I went to go take a couple of Aspirins (I don't know if that was a bad idea or not) and iced my head. About ten minutes after the incident I felt a bump forming on the parietal lobe area of my head as that was where his knee hit me. I told my mom and she's just trying to wink off a head injury which can be very serious. I haven't been nauseous yet and this happened six hours ago. Should I be concerned?