1995 4Runner knocking noise after oil change and now wont start

Hey again!
So today I did an oil change, nothing new for me since I’ve owned the car for a little over a year now. Changed the filter out, got everything on nice and tight and put back the 5 quarts of oil. Car ran perfect afterwards on my test drive. Went around town and after about an hour I started to hear a knocking noise that would increase with my rpm’s- I stopped and checked that my oil level was slightly low, and put another third of oil into the engine. Drove home and parked it. I inspected the engine and saw no sign of leaking oil, went to crank it back up and it will not start. Just inconsistently turns fast to slow, I didn’t want to force it so I locked her up and came in for the night. I’ve researched and found some pretty scary (for my wallet) things about this issue- but what I cant figure out is why it drove fine for a good while after the oil change? And seems to have plenty of oil? And why it now wont start?