1)
It origins from lol. People say lololololol (as lol many times) and sometimes they start with o, "ololololol"
The ol has been called ohl cause of the way it is pronounced.

2)
It is also being used as nothing.

Got the covid-19 vaccine

Short-hand for the Ontario Hockey League. This is the testing grounds for North America's best and brightest NHL potentials. Popular high-school girls are magnetically attracted to the male players for no clear reason other than the fact that they play hockey in the O. These girls often travel great distances to attend hockey games and surrender all human contact with their peers.

This "brain-drain" of popular, good-looking girls from high-schools is a hurdle for anyone wishing to go out with the "hot girl."