My 7m/o son has been on cimetidine 33mg/5ml bid for 2m now, & has had 2 yeast infections since he started it, is there a link?

Hard to tell: Yeast infections are not listed as side effect of Cimetidine but i can tell you that Cimetidine is not a common drug to use nowadays. It seems to have more side effects than other medications in the same class such as ranitidine or famotidine. Unless there is a compelling reason for him to take this particular medication, ask his doc to switch it to a less aggressive but similar effective one.