Gosh, I took Gabapentin for about 4 months. Plus I was started on 200mg twice daily but that wasn't enough and it was increased in stages until I was taking 500mg 3 times a day. This is usual and was, finally, effective for me. I took that dose for about 2½ months if I remember correctly. I then titrated off it in a routine of my own making and it took me another 1½ months to do that. So I suggest you go to your GP who might understand the usage of Gabapentin a bit better than did your surgeon!
If you find a dose that works, you may not have to take your oxycodone any more anyway. And you could also supplement with Tylenol 1,000mgs 4 times a day.
And as far as the discolouration on your knee is concerned, I'd just call it blotchy and is a byproduct of bruising.