'Road Trip' Star's Widower -- Birth Control Pills Killed Her ... and I'm Suing

"Road Trip" star Mia Amber Davis -- who famously played the big girl -- was TOO OBESE to have been on birth control pills and died as a result ... this according to her widower, who's suing Mia's doctors.

Mia passed away back in May 2011 as a result of a pulmonary embolism ... one day after undergoing knee surgery.

But in his lawsuit, Mia's widower claims ... in the months before the surgery, Mia's OBGYN prescribed her birth control pills such as Balziva and Zenchent ... "drugs that greatly increase one's risk for a pulmonary embolism, especially when combined with [Mia's] other risk factors."

Mia's widower lists "obesity" as one of Mia's significant risk factors.

Mia's widower claims his wife's doctor SHOULD HAVE suggested condoms or other methods of birth control as an alternative ... because the drugs "greatly increased her risk for a pulmonary embolism and ultimately caused her death."

To make matters worse, Mia's widower claims Mia went to a family practitioner on April 18 to complain about knee pain. The doc allegedly cleared Mia for knee surgery ... despite a number of risk factors, including obesity, hyperlipidemia and the fact she was on Zenchent.

Mia's widower claims the doc "should have advised [Mia] to eliminate some of her other risk factors prior to clearing her for the surgery."

Mia underwent the surgery on May 9 ... and died the next day.