Wow, that stinks. I'm sorry you are having to deal with feeding issues. It was and is so frustrating, stressful, and depressing for me.
We had to learn to put in an NG tube before our baby was discharged because she wasn't the best eater. However, she didn't need it at home. Well, not really. When she stopped taking bottles, she was readmitted.
My baby was a 26 weeker. She needed a specialty formula due to milk protein allergy. After she was switched, she took her bottles without a problem (solid food is a whole different problem). Ask your baby's doctor if you think you want to try a different formula.
I'm sending you good vibes and hope the feeding faerie visits. (They told us in the NICU that one day they just start feeding like a faerie visits and poof... they eat.)
Please let us know how he does. Hang in there!