Knee pain

When I was in 8th grade I fell down some steps and landed on brick and it took a big (quarter size) chunk out if my knee. I was terrified of getting stitches so my parents didn't make me go to the doctor (should have, I know) so I just wrapped it up for like 10 weeks. I'm not very active, SAHM, so I just layed around besides the normal cleaning and cooking and what not but on the first of Feb. I got a fitbit so I've been moving ALOT more. I've been getting a least 10,000 steps a day if not more and before it was maybe 2000. I've never had trouble with this knee until now and I swear by the end of the day it's killing me. It just throbs all night. It feels better in the morning, only hurts a little during the day but when I lay down at night it is extreme. I have no idea what's wrong with it since I've never been to the doctor about it. Should I go now or just put ice on it, take pain meds etc. and slow down a little on the activity? Anybody got any idea what it may be? TIA.