ANGLETON, Tex. (CNN/KPRC) -- Police in Texas say a mom killed her baby and she apparently told police this wasn't the first time.

Angleton police say 20-year-old Kristi-An Walker is facing several felony charges, including murder, after confessing she killed her 6-month-old son. Sgt. Kirk Coleman with Angleton police says, "She was irritated with the crying and all that kinda stuff. It got to her and so she said she just couldn't handle it."

Investigators say Walker, who also has a 3-year-old son, called them to a home in Angleton back in June, saying that her infant was unresponsive and was performing CPR until help arrived.

He was transported to Angleton Danbury Hospital where he died a few hours later from severe head trauma. Police said Walker would later admit that she wasn't actually trying to save her baby at all. Coleman says, "According to her, she didn't actually do CPR. She pretended to do CPR."

But that's not all she admitted to. Police says she's done this before to another son who was 4-months-old when he died from her abuse in Freeport last April. Coleman says, "She claims on both occasions she would throw the kids up against the wall. She would throw them in the baby seat. She would bump them up against furniture and stuff like that."

Freeport police have now charged Walker in connection with that case and perhaps most shocking of all is police say Walker is pregnant again. Coleman says, "She is being monitored at the county jail for the safety of the unborn."

Walker has been charged with murder and two counts of felony injury to a child. If convicted, she could be sentenced to up to 99 years in prison for each charge.