So the problem with the canadian system (im canadian) is docs almost never want to order an MRI for this kind of stuff. Also most GPs dont actually know anything about the musculoskeletal system.
So you say knee sprain, which means absolutely nothing in the real world.
How did you hurt it?
Did it pop or click? Did it swell up after you hurt it?
Can you walk? Does it give way? Has your knee ever given way?
Etc etc etc...
X-rays will only reveal bony stuff, so in the knee, it's basically fractures and arthritis and arthritis isn't always painful.
MRI will show soft tissue and blood flow to the area.
So when you say knee sprain, i think ACL, MCL, LCL, Meniscus etc etc etc....
You want to narrow down that list and proceed appropriately. If you have insurance i'd just go get an MRI. You can see a PT but not many PTs in canada can handle alot of this stuff. You can't treat what you dont know, i mean you can e stime ultra sound stretch this to hell, but if you did some major damage, it's not gonna get better.
When someone says it'll be better in 6 weeks that's because the body usually takes 4-8 weeks to heal stuff, if it can be healed by the body.