MILWAUKEE (CBS 58) -- A mother is grieving the loss of her son just days after he died unexpectedly.

Christopher Anderson, 13, passed away in his sleep after suffering from a respiratory illness. Monday, Shalisa Hamilton learned that her son's official cause of death was meningitis.

"Christopher was a wonderful kid," Hamilton said. Christopher loved to play video games and was a 4.0 student. His mother says he was always respectful and helpful.

The 13-year-old died in his sleep about a week after visiting the emergency room. "He was complaining of migraine, and he had chills and a fever," said Hamilton. During the emergency room visit on Feb. 22, Hamilton says her son was tested for flu and Covid. Following those tests, the diagnosis was viral respiratory infection.

"They sent us home with a prescription of Tylenol," she said. After the hospital visit, Hamilton says the headaches continued but she didn't know her son's illness was life threatening.

"By me being a working mother, I still had to work and provide for my kids, so I didn't know it was that bad," she said.

This week, Hamilton learned the cause of death was meningitis. Christopher has fluid on his brain, which caused a seizure in his sleep.

As she grieves this loss, Hamilton wonders if things would have gone differently if she'd pushed doctors to do more tests.

Her message to other parents is to be a strong advocate for your kids in the hospital.

"God really had to take him from me in order for me to wake up and realize a lot of different things," she said.

The family is planning to lay Christopher to rest this month on what would have been his 14th birthday.