I am sorry to hear that you have developed a small lump on your forehead that has been irritated by wearing your football helmet and you are worried that the repetitive pressure from your helmet may have caused the bump or made it worse. I am happy to give you some of my initial thoughts about what might be going on, but I am ultimately going to recommend that you make an appointment with an ENT (Ear Nose Throat) physician to get evaluated. They will be able to take more of a medical history, and examine you thoroughly which is really what you need to get an accurate diagnosis. You mention that you think you may have had a small hematoma (or blood clot underneath your skin) in this area from the daily pressure. While I don't want to discredit your thought, because it isn't that far off base, I must say that I would find it unlikely to have a hematoma present for 12 weeks. They typically resorb within 2-3 weeks following the initial injury
. The bump could have started out as a hematoma, and with repetitive injury the area could have healed with a hyperactive scar (as in a fibroma or a keloid) which could be the persistent bump that you feel. The ENT should be able to tell you if they think that is what might be going on when they examine you.