Better than just going to an orthopedic doctor, a general one, see an orthopedic surgeon that specializes in knees.
Most orthopedic surgeons specialize in various parts of the bone anatomy, and there are a few that are just general orthopedic surgeons, and there are some that do not do any surgery and that means you would have to see someone that does surgery if you need it.
Crazy? You be it is, but even crazier are the GP, primary doctors that think they know everything and try to treat their patients with limited, if any, knowledge of what they are doing.
Pain like you are having should never be ignored and at the very least, you should have had an x-ray of your knee done,
There are a lot of things that could be wrong with your knee, and many of them can be treated and healed with simple things like physical therapy.
BUT, until you know what is wrong, there is no way to really advise you on what is going on except to tell you to get to an orthopedic surgeon who specializes in spines.
The ortho will examine your knee, compare it to your other knee, no doubt order some x-rays and maybe and MRI, depending on what the x-ray shows.
In the mean time, until you get to the orthopedic surgeon that specializes in knees, I would suggest that you elevate your leg when you can, try some ice to see if it helps with the pain and try some advil to help with any inflammation that is there.
Don't do things that make it hurt unless you absolutely have to.
If the ice doesn't help the pain, you can try using some moist heat to help with the pain.
Good luck and keep us posted on what is going on and what you find out.
Fran