Re: Only ONE breast hurts!
Sometimes there are invisible physiological differences between breasts which can make latching on one side more difficult than the other. Often one nipple is a little shorter than the other even when completely stretched out, which means that the baby cannot get the nipple quite as deep into his mouth. And anytime the nipple is shallow in the baby's mouth, it can get compressed and pinched. The good news here is that babies grow, and eventually the importance of these minor physiological issues diminishes. A bigger mouth can achieve a deeper latch, and can achieve it every single time, regardless of how long the nipple is.
Some of the things you describe make me think it would be a very good idea for you to see a lactation consultant, preferably an IBCLC, for some hands-on help. The fact that your nipple became very large and red- that could indicate a plugged duct or an infection or blister or something a little less run-of-the-mill than a simple poor latch.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"