Custody..

I have physical custody of my one year old, from January 18th 2018 to January 24th 2019, my sons dad has only seen him a total 13 times (I have a list with dates), he doesn’t help with childcare either, he works, but he’s more focused on his soundcloud music that isn’t going anywhere. When I tell him he needs to do his half since we have joint custody (he signed the birth certificate), he tells me I’m messing with his relationship with his son for “clout”. I’m 17, and I’m a single mom who has to make money while I raise my son, he’s 20 with a job who does nothing for his son but FaceTime him for 10 minutes. So my question is, what do I need proof of to get full custody? What will help me in court? What do I expect?