Stocks fell back into the red on Monday morning after sales of existing homes hit a three-month low. 

The S&P 500 was down 0.13%, the Dow Jones Industrial Average fell 0.12%, and the Nasdaq was flat. 

The number of existing home sales in February tumbled 7.1%, a symptom of high prices and lower inventory. Sales fell to a seasonally-adjusted rate of 5.08 million, according to the National Association of Realtors. Economists had expected a reading of 5.3 million. 

Wall Street last week stretched its winning streak to five weeks, a record not seen since October last year. Investors can thank the Federal Reserve, which inspired the bulls after a comfortingly dovish statement and press conference mid-week. Stocks are currently trading at 2016 highs.

But a Fed rate hike could come sooner than some anticipate. San Francisco Fed President John Williams said the economy is "looking great" and that an April or June hike isn't out of the question. The central bank raised rates for the first time in nearly a decade in December. 

"All else equal, assuming everything else is basically the same and the data flow continues the way I hope and expect, then April or June would definitely be potential times to have an increase in interest rates," Williams told Market News International. Williams is not a voting member of the Fed this year. 

Crude oil edged higher, shaking off earlier downward pressure. Traders' confidence was undermined on Friday after Baker Hughes reported the number of active U.S. oil rigs rose by 1 to 387 in the past week, the first increase of the year. West Texas Intermediate was up 0.41% to $39.60 a barrel. 

It was merger Monday with several deals in the works. Hot takeover target Starwood Hotels (HOT) agreed to a raised bid from Marriott (MAR - Get Report) . The new offer values Starwood at $13.6 billion, above an offer from Chinese company Angbang Insurance for around $13.2 billion. Starwood shares climbed 2.5%.

IHS (IHS) announced plans to merge with Markit (MRKT) in an all-stock deal worth more than $13 billion. IHS will own around 57% of the company, while Markit will hold the remainder. The combined company will be named IHS Markit and will be located in Markit's headquarters in London. The deal is expected to close in the second half of the year.

Sherwin-Williams (SHW - Get Report) fell 2% in premarket trading after agreeing to acquire Valspar (VAL - Get Report) in a deal worth $9.3 billion. Sherwin-Williams agreed to pay $113 per Valspar share, a 52% premium to its Friday close. Valspar shares were up more than 25%.

Valeant Pharmaceuticals (VRX)  rose 1.3% after announcing plans to replace J. Michael Pearson as its CEO. Pearson has overseen a rough couple of months in which shares have tanked on an investigation into accounting inconsistencies with its pharmacy partner Philidor. The company also said Monday it appointed activist investor Bill Ackman to its board. 

Apple (AAPL - Get Report) will hold an event at 1 p.m. EDT Monday at which tech industry watchers say the tech giant could unveil a new iPhone model. Analysts predicted the tech giant could reveal a smaller four-inch phone to pad out its smartphone line. 

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