In terms of your grades, although your earlier years aren't particularly competitive, having achieved a 3.9 during your first semester means that you have the ability to handle academically challenging material. I would say that it isn't terribly uncommon for students to have weaker marks during their first two years at university, so again your not alone in this area of your application.
Although medical school admissions are hilariously competitive, each school has their own method of selection, and place emphasis on different aspects (and years) of an application. To you're point about you wanting to be a good doctor - you're right in that being an knowledgeable doctor is important, but there are other characteristics (i.e. compassion, empathy) that are just as important to the practice of medicine, many of which come from your life experiences.
I would also say that as tempting as it is to be on this forum to see what is considered as competitive, you should try and avoid this forum during your academic year. University is challenging enough , and having that added stress won't help your mental health. It may help to view the pre-med path as a marathon, not as a sprint (how I've heard it described) - in that, focus on the challenges that are immediately ahead of you, and think about the next few miles when they appear.
(I'm not saying this next part to detract from your goal of medicine, but just to help shed some light on potential options - not just MPH) there are also the many allied health profession programs (i.e. physiotherapy, occupational therapy, audiology, speech-language pathologists, pharmacy, optometry), and professional programs (i.e. Law, Dentistry).
I hope that I was able to help with some of the uncertainty, but if in the likely event that I haven't, I would suggest that you reach out to someone you're close with (i.e. family member, friend) and share how you're feeling. You're mental health is important during this process. If one day you hopefully do get accepted, having that social support is just as critical in medical school as it was before. Burnout is a serious problem and you have to be mindful to take care of yourself.
and all the best with your second semester =)