Stasis can take a while for a bunny to get over completely, but you shouldn’t need to keep going to the vet again and again, esp not since your bun has shown improvement (eaten pellets, pooped).
Do you have simethicone (baby gas drops)? If not, I’d advice you to get some. It’s OTC and not pricey and available just about everywhere I think, if you’re in the USA. In Europe, you may need to go to a pharmacy.
You can give simethicone several times a day and combine it with tummy massages. Also make sure he’s properly hydrated by syringing him water.
This is a great aritcle that you should read if you haven’t already:
http://www.bio.miami.edu/hare/ileus.html
You can call your vet and ask for a pain-killer, Metacam is probably the best one for cases like these. They shouldn’t charge you extra for a reciept I think. Gas/stasis is painful and may make a bunny very unmotivated. The rumbling sound in his belly indicates gas. That means he literally needs to fart. Which baby gas drops and tummy rubs will help him do.
If you get a painkiller for him, make sure he stays warm though, since all painkillers lower the body temp some. You can put a fleece blankie on him or even better, sit him on your knee.
And be persistent. Don’t give up. Keep up the CC, the tummy must never be empty. And please keep us posted.