Inflation picked up slightly last month, as rising gas prices took a bigger bite out of consumers’ wallets.The government’s key measure of inflation, the Consumer Price Index, showed prices rose 0.2% from December to January, slightly weaker than the 0.3% increase economists had predicted. Rising prices at the gas pump were a key factor, increasing 0.9% during the month, the Labor Department said. Improving U.S. economic data, including stronger job growth, and tension with Iran have been driving the price of oil and gasoline higher. Gas prices ended last month at a national average of $3.443 a gallon, according to the AAA Fuel Gauge Report.