Where psychology fits in is a matter of some dispute. Like most disputes, the argument can get quite heated. There are some psychologists who will get pretty angry if you suggest that psychology is NOT a natural science. Personally, I don't think that it matters much. The abilities and the limitations of psychology are fairly well established.
Psychology is a rigorous empirical disciplne.
To argue about whether it is a natural science or a social science wastes energy that would be better spent on doing more psychological research. There are many different ways of approaching a problem. Levels of analysis is a general way of referring to these differences on the whole, because they are different perspectives on the problem. Those 3 levels of analysis are content free, because they could be applied to any field. That is, the micro, molecular and macro levels of analysis can be applied in economics, anthropology, physics, etc.