It sounds like your injury was traumatic in nature. I am seriously considering seeing a specialist to find out the extent of this injury.
Pressure comes from the swelling.
In the knee, that's usually around the patella. Aside from doing nothing, an MRI and arthroscopic surgery, if indicated, are the usual first means of treatment. Some doctors will also take X-rays. I am rather skepticle of having knee surgery. From my experience, the vast majority of runners will return to their sport following surgery.