Vomiting/Intro/Long/Please help!

My almost 7 month old son was diagnosed with reflus at 6 weeks old and has been on Zantac or Prevacid ever since. Around 3 months we were told he had a true lactose intolerance by the doctor (not our regular pediatrician) and that I needed to stop breastfeeding and go on straight Nutramigen (we were supplementing with it already). We mixed in rice cereal to help with the reflux as well.

All was well with the world from about 3 months old to 6 months old. At around 4 months old we began to introduce solids. He wasnt a fan of rice cereal, so we just dove on into an array of Stage 1 baby foods. We introduced them like we were supposed to, one every few days and watched for reactions. At one point around 5 months he had some eczema shortly after eating sweet potatoes, so I made a mental note and it improved so we kept on trucking.

Right before his six month appointment he was being seen by the doctor (again, not our regular Ped.) for the babys first ear infection and we got the go ahead to try Gentlease rather than expensive nutramigen.

 We began by slowly adding it in with the nutramigen. All seemed fine for about a week and then the baby got what we thought was a stomach virus. He had runny, watery BM's, fever and vomiting. Then he started refusing to eat period. We fed him bananas and as much nutramigen as he would take and he slowly began to sleep through the night, eat better, not be lethargic and in general happier.

So we tried round 2 of switching to Gentlease. We also started with Stage 1 foods like carrots, squash, and peas. Again, no problems at first but within a week he began vomiting again (started out every bottle, then just one bottle, usually around 6 pm) and we thought he had re-contracted the stomach virus (all of the kids in his room at daycare had it.)

Our regular ped said to stop with the gentlease and put him on straight nutramigen with no rice cereal, solids, nothing. We did that the past 6 days and finally two days ago he was happy, sleeping through the night, AND VOMIT FREE, playing and gaining weight. Daycare told us he was getting upset when the other kids were eating because he wanted solids too so I decide to try squash last night.

He ate a whole Stage 1 container of squash, ate his usual 8 ounces of Nutramigen and slept 11 hours no problem

This morning when he woke up he was craky again (much like when he was possessed from the "stomach virus") and I had a feeling things were headed south. After his 8 ounce breakfast bottle he coughed a little and puked. While my husband was washing the puke off himself and I was holding him he leaned over (no coughing) and puked out the entire contents of his stomach. Then the poor baby cried like something was hurting and closed his eyes like he was sleepy and wanted to nap on me.

We bathed him, then he saw a bottle, freaked out, so we gave him another 8 ounces. He slurped it down and kind of resumed life per usual. Still a little fussy and not himself, but I was able to put him down to play while I ate breakfast.

So, I am at a loss. Is he allergic to squash? Food in general? Did his cough cause him to vomit and then the nasty taste in his mouth cause the second episode? Does he have a brain tumor (unlikely I know, but google is a scary place). Is this just how he reacts to teething.

Interesting to note: at the start of BOTH weeklong vomiting sessions by the end of the week, a tooth had visibly cut through the gums.

Obviously have a call into the doctor, just wanted some insight.