In common usage, they all mean pretty much the same thing. In a specific philosophical or religious context they might have distinct meanings, but as Mitch says in his comment, if you want to get into that this probably isn't the right site.
I found at least one dictionary that listed meager as a definition of paltry, suggesting that the two words could be used interchangeably in some contexts, particularly if you are talking about an amount.
However, if you look up both these words on Wordnik, you see some subtle differences in their meaning.
Paltry suggests something is contemptible, unimportant, and insignificant; while meager suggests something is deficient or scant.
When applied to a salary, then, a paltry salary wouldn't necessarily be lower than a meager salary, but it might suggest that the wages were insultingly low.
Although Wordnik lists both words as "equivalents" (you see that at the bottom of the page), the synonym list varies rather significantly. Synonyms for paltry include: worthless, contemptible, despicable; synonyms for paltry include: barren, gaunt, and impoverished.
I strongly suggest looking at both pages on Wordnik, as those two web pages can provide much more information than my meager contribution.
Best Answer
Perhaps "over and over again" has a slightly more negative connotation, in that the repetitive behavior is both undesirable and unnecessary.
But the difference is very subtle, and either expression would serve in the majority of situations.