Well, they are small to begin with, so for him, that is still in the "ok" range. He hasn't lost a huge amount by far.
If you do go the route of the vet, bring your Nutribac with you. Perhaps your vet can syringe a bit of nutribac slush into him while there. IF the vet recommends that, of course.
I'm hesitant to advise anything more drastic as of yet (like you doing the syringing at home) because at this point the stress may be worse then just a bit more patience and trying live pinks.
Don't panic to much just yet and don't beat yourself up. You are doing all you can. You have more options if the live feeding doesn't work.
One step at a time.
I'm crossing fingers and toes over here, that he will eat and get back "to normal".