about a month ago i injured my knee playing soccer (possible hyperextension?) on my right leg. It is now giving me problems when fully extended, more worryingly though i have a large sore lump on the outside of my leg just below my knee.

I'm slightly worried about this, if anyone knows of anyway to treat this it would be appreciated.

Best advice is to see an orthopedic surgeon who specializes in sports injuries. Chances are if it were something minor, you wouldn't still be having problems a month later.