My ex won't give my son back to me! He's been with him since October, when i lost my job & apartment?

I lost my job last April, lost my apartment that September. My son went to live with his dad (in Louisiana & i live in tennessee) now its summer & time for him to return and he's refusing saying my son doesn't want to return, which i know is all being perpetrated by him & his mother. My son's father & i were never married, we don't have a child support agreement nor custody paper because we've always gotten along pretty well. I am now working and have my own place and my youngest son has been back in my care since January. My son has lived with me since he was 1yr old up until last October, he would visit his dad in the summer. Please tell me what i can do legally & where should i file paperwork, Tennessee or Louisiana?