Medical Education US

I just signed up today, and I'm not sure how to create a topic question to directly ask Dr. Dave. But if anyone can help me out, that would be great.
I originally started as a Biology major, and did not do well in my classes. I ended up switching my major to psychology. Having had originally taken pre-med type courses and earning low grades, would you discourage my applying to medical school if I retake them and do better in them? The last time I took a biology course was at least 5yrs ago. I am currently a clinical psychology master's student, and I am thinking about applying to med school to become a psychiatrist. I have weak undergraduate grades, since my low biology course grades pulled my GPA down. When switching to psychology, i was about to improve my GPA profoundly. My plans are to pursue a PsyD or PhD, eventually. And during this time that I'm in my master's program, and potentially in a doctoral program, I want to take one pre-med course per semester, since I am already enrolled full-time as a current student graduate student (since it's my current priority).

Any suggestions? Advice?