Hit a Brick wall?!

Well.. Last Thursday he was weighed and lost a couple more onces. WHY !? I honestly feel like I'm doing everything I can do and he still is a tooth pick! Will he ever be a big boy like Tripp?! I don't know and it doesn't matter Fox is Fox and Tripp is Tripp. But no one can convince me that a baby losing weight is normal ! The doctors do not think this is normal and are very concerned. Actually his new Doc is amazing and calls me on a daily bases. Since we agreed to deal with his issues out patient she wants to make sure he's okay:) What I don't need to hear is a friends of friends of this girls co workers daughter who is such weight etc etc..These situations aren't mine, he wasn't small he was freaking born 8 lb as 36 weeks! And hasn't gained a single oz in 8 weeks! And has lost weight, he's not "small for his age" he's not thriving... This kills me. I feel like I'm failing him.
Tonight when I was changing Fox, Tripp and Everly were pointing at his scar saying "boo boo" and "oh no" like usual. Then Tripp ( newly in love with numbers) started counting Fox's ribs. My baby:(
Well his next weigh in is Thursday but he's been "off" and not eating the 33-35 oz they need him too. I don't think he has lost much more though because I think his body has platoed. He is now on another hyperhallogenic formula but fortified to 24 kal. I'm basically writing this week off. Fingers and toes crossed he doesn't really lose tho:(
My posts are so depressing lately but this is our reality. This is always in the back of my mind. However amazingly Fox is right on track developmently and is even standing up leaning / holding on ( if u put him there, he can't pull him self up,obv.) We fill our days will swimming lessons, Sunday breakfasts with best friends, park trips, choo choo trains, crafts, visits to the toddler gym, shopping trips, lots of walks etc... Everything is perfect expect my youngest sons health.