I had a very similar story with my DD2. She would b'feed and then immediately I put her upright, she would projectile vomit pretty much the entire contents of her stomach.
I'd been to the doctors about it (from day 1)- they didn't offer much help (only infant gaviscon which also wouldn't stay down). She'd cry and scream and was obviously uncomfortable, but it became so normal that I didn't even notice it anymore.
It wasn't until I visited family that my aunt (a midwife) said she thought I should pop along to our local breastfeeding cafe (where there were HVs) for some advice. I felt really bad as I felt I'd neglected her in some way - but like I said, it had become the way of life and was 'normal' for her.
As luck would have it, there was a Lactation Consultant visiting from the local hospital that day so I had a chat with her about position/feeding/my diet.
She asked if I drank a lot of coffee (I didn't and still don't) but this triggered something in the depths of my memory. I did (and probably still do) eat quite a bit of chocolate and I seemed to remember that there's theobromine in chocolate which can mimic an excess of caffeine in the diet. (She looked in a La Leche League manual - and the symptoms were spot on - restlessness, arching back, reflux etc). She advised me to stop eating chocolate, or at least to cut right down.
I also had a very fast letdown reflex so the milk pretty much gushed down DD2's throat and she had a job to keep up with it. She advised me to put DD2 in a more upright position for feeding, rather than laying down.
In addition to that, I was also tandem feeding - I was feeding my 2 year old - and I asked if this was a problem (my MIL insisted it was, as she said, my milk was too rich for the baby and this is why she was sick so much). The Lactation Consultant said this wasn't thought to be a problem - and offered some research into this - she said that the thinking was you fed the toddler only from one side, and the baby from the other and never switched - the idea was that your body 'knew' what was needed for each child.
DD2 was about 16 weeks when I saw this lady. Also around that time, I started giving her very small amounts of baby rice and I also began a baby massage course - and I concentrated on the colic routine.
Shortly afterwards, (really, within a week)the projectile vomiting/reflux/screaming and crying stopped. I won't ever know which single thing or combination of things worked.
Does any of that sound familiar to your situation?