it sounds although you have fluid in your knee joint - an effusion - this is always abnormal. you should see you dr so he can examine you and arrange an X-ray of your knee. if this is normal then he may also want to order an MRI
scan. there are many possibilities to explain you pain from a fracture
in your knee joint to a meniscal tear. In the meantime an antiinflammatory medication may help with the pain and swelling.