After a strong start to the season, sales at stores have fallen for three consecutive weeks. That puts a lot of pressure on retailers to get shoppers into stores in the final days of what’s typically the busiest shopping period of the year.

Sales at U.S. stores dropped 3.1 percent to $42.7 billion for the week that ended on Sunday compared with the same week last year, according to ShopperTrak, which tracks data at 40,000 locations. That follows a decline of 2.9 percent and 0.8 percent during the first and second weeks of the month, respectively.

The numbers, which don’t include online sales, are another challenge in what has largely turned out to be a disappointing holiday shopping season for stores. The two-month period that begins on Nov. 1 is important for retailers because they can make up to 40 percent of their annual sales during that time.

Retailers started the season cautiously optimistic after a strong start in November — ShopperTrak said sales were up 3.4 percent for the month. But in the final days, retailers have found it increasingly hard to attract shoppers into stores even though some like Toys R Us have rolled out big discounts, while others like Kohl’s have stayed open for dozens of hours straight since the weekend.

None of that seemed to lure shoppers. At the Garden State Plaza Mall in Paramus, N.J. on Saturday, Abercrombie & Fitch, AnnTaylor and Express had 50 percent sales, while Aeropostale was discounting its entire assortment up to 70 percent.

Still, Barbara Jackson, 45, was spending cautiously. She said she’s capping her holiday budget at $1,500 — half of what she spent last year. That’s because Jackson, an aide to the elderly, is earning less than last year.

“I am more budget conscious,” Jackson said.

Karen McDonald, a spokeswoman at Taubman Centers, which owns or operates 28 malls, estimated that business for the week that ended Sunday was unchanged to mid-single digit percentage growth compared with a year ago.

“I felt for sure it was going to be gangbusters. But it was just OK,” McDonald said.

Shoppertrak estimates that holiday sales at stores so far are up 2 percent to $218.4 billion compared with the same period last year. That’s below the 2.4 percent forecast for the two-month period, but the company is standing by that estimate with a few days left before Christmas and a little over a week before the season ends.

The National Retail Federation, the nation’s largest retail group, also said it’s sticking with its forecast that sales in stores and online will be up 3.9 percent to $602.1 billion.

But even online sales, which had been a bright spot for much of the season, aren’t growing at the expected pace. Online spending from home and work desktop computers in the U.S. from Nov. 1 through Dec. 15 was up 9 percent from the same period last year to $37.8 billion, according to the most available data from comScore.

That’s below the 14 percent growth that the Internet research firm is forecasting for the season. The company still expects online sales to grow at that pace for the season, but the category only accounts for about 11 percent of spending in the three months that include the holiday shopping season.

Final sales figures for the holiday shopping season are expected in January.