I can only do 2 passes WTG, anymore and my face gets sore. Is this a technique issue or will my face get used to it?
I have a Slim adjustable set on 3 at the moment.
I'm almost 100% positive that this is just a technique issue. Concentrate on learning proper blade angle. The steeper the blade angle, the more you are just scraping the blade across your face. That leads to a LOT of razor burn. Moreover, if you just recently switched from cartridge razors, I guarantee you're pressing down on the blade, even if you think you're not. Seriously, with DE shaving you have to unlearn soooo much of the bad habits from cartridge shaving.
Hang in there, and focus on your technique. It will take some time, but you will get the hang of it. And, believe me, it is so worth it!
Welcome to B&B, by the way!