Knee feeling after long ride with road bike
If you ride further or faster than you're used to, then some weariness in the legs is normal and should pass within a couple of days. I rode my biggest ride to date a couple of weeks ago and when I got home I nearly lost my balance walking around the house as my legs were a bit weaker than I expected. With a couple of days rest they were back to normal, however.

Besides rest, what can help your recovery is static stretching (not bouncing or bobbing). Here are some suggestions for knee stretches. 

As others have suggested, a higher cadence (therefore a lower gear) may help, even if you can't measure it precisely. I have a knee injury from running, so I change down a gear the moment it gets uncomfortable.

For bike fit, trial and error can work well, here's a link to some simple bike-fit tips which may help you move in the right direction.

All that said, if discomfort becomes pain you should obviously stop doing what hurts and get advice from a physio, ideally one with cycling expertise.