Sorry I only saw this email this morning! Arching and refusing to nurse can be signs of acid reflux and/or food allergies. It can also be a sign that your baby didn't like the flavor of something you ate. With the arching of the back, I think these are more likely reasons than just deciding he no longer wants to nurse. I needed a lactation consultant while nursing, and she told me babies sometimes take the same milk from bottles or cups, even if they won't take it from mom. They don't understand why this is. I would look at any changes you've made to your diet first before giving up!
If you don't feel your pediatrician is helpful, my pediatrician was very supportive of breastfeeding, and provided much valuable information to me. He's Dr. Straughn @ Forest Lane Pediatrics. His information is in MamaSource directory, and I've seen many other moms als recommend his group.
Also, my lactation consultant was Judy Eastburn in Richardson. She sees clients in her home @Hillcrest and Arapahoe, and she's intelligent and caring. Wonderful! Her number is ###-###-####. Good luck!