Here's a list of public health jobs that is maintained regularly by Emory. Some jobs are specifically for MDs/DOs and PhDs while others are for MPHs. Depending on your interests, you can work in research, consulting, administration, epidemiology, etc. Teaching, in most cases, requires a doctoral-level degree.
http://cfusion.sph.emory.edu/PHEC/phec.cfm
Why public health over psychology? You can always do both, as an MPH should not take longer than two years of full-time studies. A PhD or PsyD in clinical psychology is usually five years, including the internship year. The combination of a clinical psychology PhD/PsyD and MPH is becoming increasingly common among psychologists, with research interests spanning clinical psychology, health psychology, epidemiology, health services, and preventive medicine. Here are some examples of what you can do with a doctoral degree in psychology (doesn't have to be clinical psychology) and an MPH:
http://www.commed.uchc.edu/faculty/babor/
http://www.ucsf.edu/ocim/faculty/bio_moskowitz.html
http://www.cas.suffolk.edu/psychology/recklitis.html
