Hi there! My daughter had a much milder milk/soy protein allergy, and she also sees a GI specialist at Dupont (we see Dr. Molle-Rios). I TOTALLY understand your frustration with Drs, my daughter has many specialists on top of her pedi due to issues when she was little, and I remember getting so frustrated because it seemed like despite all the tests, appointments, phone calls, etc, I still felt clueless as to what was the best thing for my daughter. So much of their advice conflicted with each other and my own instincts, and there were so many tests and medicines that were all "inconclusive".
My only advice would be to trust your instincts! The Drs there are good, but its YOUR child, and you are around them 24/7. They make money off of repeated visits and testing, and other than being professionally responsible, have no real tie to your child. Also, if you trust your pediatrician, always get their input! We LOVE our pediatrician (Dr. O'Mahoney at Broomall Pediatrics if you're close) and everything (specialist visits, tests, prescriptions) goes through her. She has known my daughter since she was born and I trust and agree with her philosophies on treatments.
After months of frustration with back and forth with Drs like you described, we finally (with our pedi's blessing) backed off on all the searches for treatments and diagnosises, and just gave her a few months to grow. She has since thrived and every day is healthier than the day before! I'm not at all recommending ignoring any medical professionals, just to be patient, it seems that so many of these issues improve over time. I'd be in no rush to start solids, maybe more formula would help?
Anyway, not sure I've really been much help, just wanted to share that I COMPLETELY understand your frustration. You want so badly to do the right thing for your baby (this is our first child as well), and its so frustrating when it feels like no one is really sure what the right thing is...
I really hope things improve for your son, my daughter was on Nutramigen (the enfamil equivalent of Aluimentum)until about a month ago, and is now able to take Similac Sensitive with no issues. Granted, her allergy didnt seem as severe as your son's but there is a light at the end of the tunnel, and these little guys, when given a chance to just grow and get healthy DO grow out of these issues!
Good luck!!