NEW YORK — Stocks shifted between gains and losses on Wall Street Wednesday, keeping the market on track for its fourth monthly loss this year. The S&P 500 was down 0.2% as of 2:45 p.m. Eastern. The benchmark index has been volatile all week, and is down about 20% for the year as investors worry about inflation and rising interest rates. The Dow Jones Industrial Average rose 74 points, or 0.2%, to 31,018 and the Nasdaq slipped 0.3%. Small company stocks fell sharply in a signal that investors we