Baby sick

Hi my baby was five weeks early after a terrible pregnancy, when he was a week old he was sick and held his breath till he couldn't breath and ended up in intensive care. Since being home he is still sick not all the time sometimes it can be weeks between. I don't think uts normal as it not protectile but will come up and out of his nose (which scares him) alot. Lucky now he doesn't panic and I'm able to reassure him but it's still happening at 11 weeks. Has anyone else been thought this? Or have advice please