Clogged duct?

My son is 4 days old today and my boobs hurt sooooo much! He only eats out of one boob at a time which makes things a little harder but i do have a breast pump that i can use. My question is, what are some signs of a clogged milk duct and can it happen this soon? My milk is just now starting to come in. Almost half of my left boob gets really hard and sore to the touch but its not any warmer than the rest of the boob. I dont have a fever or any other symptoms. This is baby #2 but i just dont remember it being this painful the first time. Could all of this really just be normal and if so, why doesnt my whole boob or even both feel like that instead of just one side of one boob? Thanks in advance!