My 9 1/2 week old breastfed baby has been screa...

My 9 1/2 week old breastfed baby has been screaming as soon as I sit him up after a feed. He screams and screams and arches his back until he burps and then brings up mucousy milk. Even after burping he still screams and only stops after this mucousy milk comes up and then he sounds so relieved. It is so distressing for both me and him and it breaks my heart when it happens. It doesn't matter if he's fed for 5 minutes on one side or if its 20 minutes - it doesn't make a difference. It's been going on for the last 2 or 3 weeks. He is on Zantac for possible reflux. Is it the reflux that is causing this pain? Wind? or something else. Has anyone else been through this? Thanks