Why is my major so competitive?

I'm a premed biochem major. I'm not too bright, but I am a hard worker. I didn't do so well in freshman year because I really didnt try. But after freshman year, I became more competitive. I realized that these guys are competing for the same seats as me for med school. So I started working hard. I have like the worst memory ever. I cannot remember anything even after I just studied it. That made biology a challenge. But I forced myself to learn the material. It took months of nonstop studying and hard work and I got A's and A- in my bio courses. Same for physics and orgo. Eventually my rate of learning increased. Yeah, I got a bunch of good grades, but I had to work 10 times as hard as other people to get the results. But now I noticed a transformation in my personality. I am reluctant to help people now. If I teach other people what I know, then I am hurting myself because they would a better grade than me and eventually steal my seat in medical school. I can't let that happen. So if I know information, I keep silent about it, unless someone prompts me for help. I once had a friendly personality, but now I became very aggresive and competitive. I mostly act like this to people inside my major, but sometimes even in everyday life. I have become sick and twisted, but I must do this if I am to get into med school. I gotta beat these guys and get higher numbers than them no matter what it takes. Maybe one day when I get into med school, I can be happy and wont have to fight with other people for a seat. Maybe some day, I can learn to coexist with these people. But right now, that is not the case, and I must fight my way to the top- so I can live a better future. Am I wrong for thinking like this? I'm sure I'm not the only one with this mentality