Unless it happens in .001% or .0001% of those on propecia, it would have been listed as a side effect. THe chances of remotely significant side effects on propecia are about 2%. People report more side effects because:
1. people losing their hair are WAY more paranoid and actively looking for possible side effects. I take it that you're losing hair; I bet you can recall being more than a little paranoid since it started.
2. sh*t happens. If your breasts get bigger, maybe you should go do a little cardio before racing to hairlossforum.com and reporting that propecia made you grow breasts. Sometimes your balls are sore for a while for no apparent reason, sometimes your nipples are sensitive. But the fact is, propecia causes sides in just 2% of people.
don't let threat of sides or even a few people reporting weird sides scare you. fact of life: sh*t happens and people are paranoid. If even the exceptionally paranoid people on this site such as myself haven't mentioned it, then REALLY don't worry about it.