I would strongly suggest you see a rheumatologist to rule out OA, RA and PsA before accepting a single diagnosis of "weak quads."
I have had PsA for 47 years, diagnosed when I was 18, and your symptoms are exactly the same as mine were back then. (I have no idea what shape MY "quads" were in at the time)
While it was good your doctor took X-rays, it can take many years for visible evidence of arthritic damage to appear.
Those are my thoughts and I wish you the best.
First, let me tell you I'm happy you found us here on the Arthritis Comminity!
I'm so sorry to hear that you are experiencing these problems with your knees. I understand what you're going thru suffering with this pain at such a young age! My Doctor's believe that my osteo-arthritis began when I was a teenager. By the age of 28, my Doctor's were prescribing a THR(Total Hip Replacement). Whether or not your pain turns out to be Arthritis, you definitely need to get a diagnosis ASAP so your pain can be controlled immediately!
PLEASE remember that there are NO Doctor's on this Community only we members that are experiencing the same type of problems that you are.
RubyWitch gave you some very good advice about seeing a Rheumatologist for your symptoms that you are experiencing. I have no idea which type of Arthritis you might have (if it turns out that Arthritis is what is causing your pain you are experiencing) but a Rheumatologist is definitely who will have the answers you are searching for!
I wish you the very best and HOPE you will continue to post on MH (MedHelp) and share you experiences and help others in that way.
I'll be watching for your updates. :) ......... Sherry :)