I'm writing an APA summary paper on a journal article. I am not using any other sources but that journal article. Would I need to keep citing the article throughout my paper such as putting parenthesis after each sentence? It seems a little redundant if I do that.
If this is a homework assignment, I think your best bet is to find out what your professor/teacher/boss wants and do that, regardless of what any APA style guide tells you.
The best actual style guide answer I can give is "if you are in doubt about whether to cite a source, cite it" and "if you go more than a paragraph without citing ... make sure you have not left out a citation." (Mitchell, Jolley, & O'Shea, 2010)
I have written many APA style papers and, in my experience, nobody has ever complained about having too many in-text citations or having repeated citations. If you really want to cut down on repeated in-text citations my suggestion is to cluster ideas from the same authors into a paragraph and make it clear that the paragraph is discussing their ideas.
Mitchell, M., Jolley, J., & O'Shea, R. (2010). Writing for psychology (4th ed., p. 134). Australia ; Belmont, CA: Thomson/Wadsworth.