Contracted
(2013)

Pooper:
Samantha kills Nikki, her apathetic girlfriend, by choking her to death after Nikki finds out Samantha hooked up with a man at a party and Nikki confesses she's been cheating on Samantha, then bludgeons her friend Alice to death after going to her house and telling her she has nobody left but Alice (she gives Alice a bloody, gross out kiss and then kills her).  Samantha then cleans herself up (as best she can), calls Riley to come over, and has rotting, maggot-y sex with Riley and then transforms into a full on zombie as she's driving home to her mom.  She gets out of the car, takes a swipe at someone trying to help, and then, when her mom calls for Samantha to come to her, Samantha lunges at her and the screen goes black.

A little longer:
Samantha (Najarra Townsend), amid a drawn out break up with her girlfriend Nikki (Katie Stegeman), sleeps with a guy who had sex with a body with a biohazard toe tag at her friend Alice's party.  Throughout the movie, Alice (Alice Macdonald) is trying to help the police locate the guy; as it turns out, Zain, Alice and Samantha's dealer/friend sold the guy ruffies which the guy used on Samantha and effectively raped her and infected her with some kind of zombifying illness.

Samantha visits the doctor multiple times and he shames her about having unprotected sex.  Samantha's mother thinks she's started to use drugs again and wants to take her to rehab.  Alice wants Samantha to break it off officially and finally with Nikki.  Samantha's stalker/kind of nice guy Riley wants to help her but doesn't know how.  In the course of the film, Samantha begins thinking it's a terrible hang over, then a horrible/extreme period, then something more as her eyes turn red and then one turns white and milky.  Her fingernails rot and fall into the salad she serves at the restaurant she works at and she's denied entry to a flower competition she wanted to go to.

After all this, Samantha kills Nikki, her apathetic girlfriend, by choking her to death after Nikki finds out Samantha hooked up with a man at a party and Nikki confesses she's been cheating on Samantha, then bludgeons her friend Alice to death after going to her house and telling her she has nobody left but Alice (she gives Alice a bloody, gross out kiss and then kills her).  Samantha then cleans herself up (as best she can), calls Riley to come over, and has rotting, maggot-y sex with Riley and then transforms into a full on zombie as she's driving home to her mom.  She gets out of the car, takes a swipe at someone trying to help, and then, when her mom calls for Samantha to come to her, Samantha lunges at her and the screen goes black.

Thanks Linsey!