Hi knight - I'm no expert, but have had both knees replaced. What you describe doesn't sound normal at 8 weeks.

One question - what are your Flexion and Extension numbers? Ideally flexion should be 120 degrees or higher, extension should be zero or very near zero.

You mentioned you had upped your activity. To see if that's what's causing this, I suggest taking it very easy for a few weeks, ice and elevate and if you can, take Tylenol for pain. You can buy a temper-like foam device that will raise your knee above your heart lying down. You can get these things at Amazon. If the symptoms persists, then I'd see the Dr.

Pain on the side of the knee can also be caused by a tight Illiotibial Band (ITB). You can look up ways to stretch it.

I hope it resolves.