blocked tear duct

My 5 week old has had a blocked duct for a couple of weeks. It oozes yellow but only when he cries. Saw some green dried discharge - not sure if it came out green or dried darker - have only seen it come out yellow. Has anyone else experienced this? Feel like I should take him to the doctors but don't want to if its not a big deal. Have read about using expressed breast milk but scared of making the infection worse.