(Photo Credit: JenArnoldMD/Twitter)

Just three weeks after she revealed she had a rare form of cancer, TV personality and neonatologist Jen Arnold has begun chemotherapy.

Today, she tweeted a pic of herself - after already losing all her hair - saying, "Day2 inpatient chemo- sleeping alot, liking new anti nausea med this time, & looking to get home today!"

The picture, which was taken from the hospital while Arnold, 39, was being treated, shows the "Little Couple" star being brave and flashing a smile.

Read: 'The Little Couple' Star Jen Arnold Has Cancer

Shortly after she announced her illness, PEOPLE magazine reported that she was diagnosed with stage 3 choriocarcinoma, a rare cancer that formed during a non-viable pregnancy she had in September.

People also reported that Arnold's treatment had been postponed for a week due to low blood counts, which allowed her to spend time with her family - husband Bill Klein, 38, son Will, 3, whom they adopted from China and a 2-year-old daughter Zoey, whom they recently adopted from India.

Related: 'The Little Couple' Star Shares Details of Her Cancer Battle

"I am very fortunate as the prognosis is very good," Arnold said when she announced the cancer. "Being surrounded by the love of my husband and our two beautiful children is actually in many ways giving me the strength to fight it even stronger."

In addition to current chemotherapy, a hysterectomy was also performed prior when a cancerous mass in her uterus didn't initially respond to treatment.