Really feeling like what did I do to myself

I was the exact same after surgery, hated protein shakes and didn't drink them.  Found out I was dehydrated and that caused the weakness and nausea too, so sip, sip, sip!  It will make you feel better.

Try PB2, if you like peanut butter. For some reason I couldn't stomach premeir shakes without adding some flavor to them. I'm no expert- my surgery was on July 20th. 

Be well!

I think you'll come to realize you're on the right track soon.  I also felt exhausted during my second week, I remember that clearly and couldn't understand at the time until I read others had the same experience.  I didn't have any issues with consumption though but I know everyone's experience is unique.  Stick to this as it will definitely get better.