I Took A Hard Fall On My Knee Two Weeks

I took a hard fall on my knee two weeks ago, it stung but didn't seem to be a big deal.
The outside of knee seamed sore to touch and slow to fully heal, but did not inhibit me in my daily activies.
Then this past weekend I was crawing around working on a trailer when my knee became painfull and stiff.
It had become quite swollen around the cap and about six inches up my thigh on that out side where the lingering soreness was. It was almost impossible to bend. I ice / elevated with some success, the fluid level has reduced and I can walk almost normal. Does it just take time for the fluid to disipate?
Why would this happen two weeks after the blunt trama?

Thanks, Dave