Groupon shares have reached their lowest point since the company has been public. As of the time of this writing, shares are sitting at $5.55, down 26.49%‎.

The nosedive occurred, following the company’s earnings release on Monday, despite the company’s 45% year-over-year increase in revenue at $568% and its operating income of $46.5 million (compared to an operating loss of $101.0 million in the year-ago period).

Analysts believe Groupon’s slowing billings growth is a major contributor to the stock’s fall, along with the company’s lower-than-expected outlook.

The billings growth rate was 38% (YoY) for the quarter compared to 102% in Q1. That’s a pretty drastic drop.

Groupon expects Q3 revenue to be between $580 million and $620 million, an increase of between 35% and 44% compared with the third quarter 2011. Income from operations for Q3 is expected to be between $15 million and $35 million, compared with a loss from operations of $0.2 million in the third quarter 2011.

Groupon shares IPO’d at $20, and hit about $30 on its opening day.