Not sure of the formula for the pressure TBH, but it sounds like you're pressing far too little for a cheddar type cheese. I'd want to press it for at least a week, turning it every 12 hours or at most every day. After the first couple of days turning it, start increasing the pressure gradually. You want it just to start weeping whey gently, not have it rushing out or it'll dry unevenly.
I'd also try dry salting rather than brining, at least at first. Use about a tablespoon of salt for each half pound of cheese, cover it liberally and leave overnight. You can wax right over the salt afterwards.