Does my puppy have Separation Anxiety?

Hello! I have a 17 week old Jack Russell, he came home when he was 7 weeks old (I know it was too early but their owner advised us to take him since mom had stopped feeding them and dad was being aggressive towards pups and had sent two to the vet). When he first came we started crate training him (he never slept in our beds during the night) but he never got used to being in the crate during the day, he will nap there during the day if I take off the top part tho.

Anyways, I’ve always known he’s too attached to me, but I though he would slowly grow out of it but I want to know what can I do to make him more independent. He’s always following me, even when I went to the bathroom he would start crying at the door (he’s stopped doing that a bit and if he cries he stops it after a couple of minutes). Before, I tried to train him by leaving the house for 1 minute, then 5, then 10 and so on, he seemed to understand and gradually stopped crying during the training sessions but outside of that he just starts crying whenever I leave. If I’m not home he usually stays with my mom or sister (and my other dog) but yesterday I went to the market and he stayed with my mom, apparently he kept going to the door and crying (lowly) my mom kept taking him to her room but he kept going back to the main door to whine.

But this is worse when he is left alone with no people, we put him in his kennel because he obviously can’t be trusted with “freedom” but I make sure to take him outside to play and I put toys and a kong with food to keep him entertained (I also leave some relaxing music playing in the background). But this doesn’t stop him from SCREAMING his guts out, he cries like this for around 2 hours and it can be heard even from way outside the house, he just screams like he’s being kicked or something and it stresses out my other dog. I don’t know how to get him used to staying alone??

Also, he doesn’t seem to cry when he’s outside without me. The dog trainer takes him out on his own twice a week and he never complains, she my mom takes him out he also doesn’t cry, and when I took him to the vet for a bath they told me he didn’t cry either. So I want to know how can I make him comfortable when staying alone at home. My other dog wasn’t like this, he whimpered a little but never cried as much as this puppy so I’m completely at lost. And if my puppy has separation anxiety is there a way to reverse it? I know it’s my fault since I’ve been taking care of him 24/7 since he came but I don’t want him to be like this forever.