How is pick order determined in draft (Normal, Ranked, and Ranked Flex)?

As the post states, I'm wondering how pick order is determined in draft. If I am playing a solo lane (mid/top) I pick in the first rotation roughly 80% of the time, otherwise it seems to be random. It has gotten bad enough that my friends comment on it unprompted. I attempt to counteract this through asking for trades or to pick for people, but this is difficult to do with any consistency in solo queue. I'm getting a bit tilted because every game I end on a tank cowering under tower for the first 10-15 min because I have to deal with always playing against a counterpick. Am I just unlucky? Is there some champ that just doesn't have a counter that I could be picking? I've picked in the first rotation 17 of my last 20 games across all roles, 19 of my last 20 top lane games (my primary role).