American shoppers picked up their spending a bit in February after pulling back the previous month. But last month’s gain was weaker than expected, and January’s decline was revised even lower, suggesting that consumers are becoming more cautious. Retail sales rose 0.6% last month after falling a revised 1.1% in January, dragged down in part by inclement weather, according to the Commerce Department’s report on Thursday. February’s number was also lifted in part by higher gas prices and higher auto sales. Excluding sales from gas stations and auto dealers, sales were up 0.3%.