My LO was like this for a few days. Try rocking him to sleep next to running water, or get the sleep sheep. It helped us a lot since it would just keep going until it turned off. Also you mentioned he's on reflux meds, have you raised his mattress 30 degrees? That helped our LO. Another thing I found that helped was try letting him nap on his stomach, but watch him while he naps. It could help him feel better.
I know you've probably tried a lot,but these are just somethings that helped our LO. He's a lot better now, and still sometimes he fights to go to sleep but it takes a few minutes before he stops crying.
Hope he grows out of this stage soon!