Chrisean Rock says she's a free woman ... writing a message to her son, Chrisean Jr., all about how grateful she is to be back with him after her arrest in a drug case.

The rapper shared the tribute Friday ... saying she's feeling blessed to be with her son just days after his birthday -- though she admits she regrets missing the first birthday of his life.

She says milestones are big markers of achievement when it comes to kids ... but, people should also focus on the love and care they provide for their kids every day.

CR's encouraging people to cherish every moment they have and trust in God ... signing off with a thank you for all the fans praying for her during this difficult period.

Chrisean's caption accompanied a sweet video of her and her son spending quality time together ... with tons of adorable pics for fans to enjoy.

ICYMI ... Chrisean was arrested back in June after walking into a Los Angeles area courthouse for a probation violation in the Tamar Braxton assault case. Adding to her legal woes, she was extradited to Oklahoma last month in connection to a drug case.

Prosecutors are accusing Chrisean of being in possession of controlled dangerous substances with intent to distribute, and failure to have a tax stamp affixed on the drugs. If convicted on both charges, she faces up to eight years in prison.

We've checked the inmate roster ... and, Chrisean's definitely out of jail in OK. Unclear why as of right now -- but, we've reached out to Chrisean and authorities to clarity her case.

Sounds like she's making the most of her time with her son in the interim.