I had knee replacement in Feb. I susessfully completed my rehab and have since been diligenty exercising and rebuilding muscle of which I've accomplished. My health is very good and I'm generally very fit for my 78 years. I weigh 152 which was my weight at 21 years. I'm verry active but I still have severe pain when I bend the knee.
What kind of pain are you having? I had 2 total knee replacements, 1st went well, 8 weeks later had 2nd done 3 hours after waking up I knew something was wrong. I told everyone in the hosp,surgeon, p.t.'s my knee/leg felt like a metal clamp lined with nails was clamped on my leg. It also feels like Ive been injected with HoT THICK gel with shards of glass. I cant even stand touching my own skin. Is your pain constant? Every second of your life? Or...only when you bend it. You must be clear when describing the pain to your doctors or p.t.'s. to get a proper diagnosis. Do not let them ignore you or tell you " I dont know what you are talking about". I got that alot until I freaked out, cried and demaned a P.T. take me seriously.
Lots of smart people on this site that can help/support you.
On balance it's probabbly not RSD or you would not have been diligently exercising. If you had RSD your knee would be shiny and swollen. Heat/cold would cause extreme changes. Touch would hurt like hell.
Just in case do not under any circumstace use ice or hot/cold water contrast.
Get to your doctor because even if there is a small possibility I'm wrong you will need help.
I would have to say if you are as active as you say you are very lucky. Like kevscar said if you were capable of being vey active and maintain it its prob not rsd, most of us have pain after we are healed but it was consistant through our whole ordeal. and yes im sure that in PT they would have put hot then cold on it and right there if it was tolerable say prob not rsd ..temperature extremes are not a nice thing for us in fact it is quite painful. i would not wish it on my worst enemy..and the color change skin change and growth of hair or loss of hair . and the pain pain pain..icould go on with that but it is far worse than tooth pain or migrains or passing a stone. and it is always going..
but again like i said many time rsd isnt the same for all so in the slight possibility you do have it get test done just to make sure. good luck