What has Nelly been up to in between record releases? According to American Express, he's been running up a huge tab on his AmEx account -- and now he's getting sued in herre.

According to TMZ, American Express is alleging that Nelly owes more than $20,000, which they've been trying to get him to pay back for months. The lawsuit, which was actually filed back in October, is asking for the full amount plus $3,000 in legal fees.

Although Nelly hasn't reached the platinum mark since 2004's 'Sweat' and 'Suit' sold a combined four million copies in the States, he hasn't been entirely absent from the charts. His 2008 release 'Brass Knuckles' and 2010's '5.0' both reached the Top 10, with the former going gold, and he scored a Top Five hit on the singles charts with 'Just a Dream' last year. So he should be able to stay on top of his bills, right?

Nelly will get a chance to plead his case in front of a judge on Jan. 9, when the first hearing in the lawsuit is scheduled to take place in Missouri. The rapper and his reps haven't returned calls for comment. Maybe he's too busy working on tracks for his next album?