How can i tell the difference between a cold sore and eczema?

The corners of my mouth are all cracked and sore, i read that a cold sore will blister and eczema won’t? Im not sue though.

It sounds like you have neither, but just chapped lips. A cold sore will, in fact, blister, and ooze, as well where Eczema seldom manifests on the lips. Chances are, some Chapstick or similar product will solve your problem.