Meaning of "down on me" in the Janis Joplin song

What does 'Down on Me' mean in this Janis Joplin song?

Down on Me
Well, down on me, Lord, down on me.
I said it looks like everybody in this whole round world,
Yeah hey yeah all right, is down on me yeah.
Yeah yeah yeah yeah.
[...]

I'm sceptical about the 'oral sex' meaning here.

Solution 1:

It looks like everybody in this whole round world Down on me

It seems like everybody in the world is hostile to, negative toward, or critical of me.

The "Down on me" refrain at the beginning can't be understood on its own, until you get to the fuller sentence. This is quite common in songs.

You're correct that it has nothing to do about oral sex, and I suspect that any explanations claiming such are either joking, or wishful thinking. That said, Leonard Cohen's "Chelsea Hotel No.2" with the line "Giving me head, in the unmade bed, while the limousines wait in the street." was about Joplin.

Solution 2:

It looks like everybody in this whole round world is down on me.

ODO on down on:
be (or have a) down on
British informal feel hostile or antagonistic towards:
she had a real down on Angela

"It looks like the whole world feels hostile or antagonistic towards me."

Solution 3:

From my experience of living in those days with people her age, her fans, and in that culture, the exact translation of, "everybody is down on me," would be, "Everybody is upset with me."

Their response to her would have made her feel 'down', or 'sad'.

Had she done something while drunk or drugged, that she was now ashamed of, and was being punished by others (through shunning, curt remarks, cancelled appointments, angry fan mail), she would feel 'down', and would say 'they are down on me', to bring her own feeling of 'down' into their feelings about her. It was an expression created by those expressing feelings while high.