CHICAGO – Rep. Jesse Jackson Jr., a once-rising political star who has been on a months-long mysterious medical leave for bipolar disorder while facing separate federal investigations, resigned from Congress Wednesday, citing his health problems.

Jackson’s resignation, just two weeks after voters re-elected him to a ninth full term, comes amid a House Ethics Committee investigation into his dealings with imprisoned ex-Illinois Gov. Rod Blagojevich and reports of a new federal probe into possible misuse of campaign money.

In his resignation letter to House Speaker John Boehner, Jackson admits “my share of mistakes” and, for the first time, publicly acknowledges that he is the subject of an ongoing federal investigation.

“I am aware of the ongoing federal investigation into my activities, and I am doing my best to address the situation responsibly, cooperate with the investigators, accept responsibility for my mistakes,” he wrote.

Jackson added: “They are my mistakes and mine alone.”

Jackson, 47, disappeared in June, and it was later revealed that he was being treated at the Mayo Clinic for bipolar disorder. He returned to his Washington home in September but went back to the clinic the next month, with his father, the Rev. Jesse Jackson, saying his son had not yet “regained his balance.”

Jackson was easily re-elected Nov. 6 to represent his heavily-Democratic district, even though his only communication with voters was a robocall asking them for patience. He spent election night at the Mayo Clinic but later issued a statement thanking his supporters