Louis Tomlinson: Baby Mama Keeping Me from My Son ... I Want Joint Custody

Louis Tomlinson has had it with his baby mama denying him access to his child, so he's now going to court to seek joint custody ... TMZ has learned.

Sources familiar with the situation tell us Briana Jungwirth has been "inconsistent" in giving Louis access to 5-month-old Freddie Reign ... especially recently.

Louis wants to be a real father and present in Freddie's life, so he's going to court not just seeking joint physical and legal custody, but a 50/50 split in terms of the division of time each spends with their son.

The One Direction singer, we're told, is paying Briana around $15k a month in child support, and a judge will now set whatever amount is deemed appropriate. Louis is also renting a $1 million house for Briana and the kid in Calabasas.