The topic of repeated measures is large and complex, and I don't think the discussion forum can really address all the issues that you need to consider. The approach to repeated measures in GLM is very different from the mixed-model approach (such as in MIXED or GLIMMIX). I recommend you read:
http://www.ats.ucla.edu/stat/sas/library/mixedglm.pdf
by Russ Wolfinger and co-author. It is now somewhat out of date (lots of new features in MIXED, etc.), but this may get you started.
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