My very first crash (caused when my DS, going down a hill in the opposite direction, on his cx bike, asked me for a sip of my water bottle, about 1 mile from my house) caused a huge hemotoma on the side of my knee. I woke up 3 days after the crash with the lump and excruciating pain. I wet to the pcp, who sent me to an ortho, who wa about to send me for surgery!!! . But, he did send me for an MRI , which showed a hemotoma (which I had self diagnosed). He drained it, and I was done. It took me a week after that to get back on the bike.
I have a calcified hemotoma on my forehead from the car door smacking into me last fall. It's small, doesn't hurt, but will make me have bangs for the rest of my life. Sometimes a tight bike helmet annoys it, but, it's OK other than that.
Get your knee checked.