I feel your pain and it will pass. I read about 4th trimester and I concluded it was a developmental thing. There was absolutely nothing we could do to cure it. It stopped as suddenly as it started if its any consolation. We spent approx 4 hours every night from 7-11 at our wits end.
The first night it happened we rushed her to hospital as we thought something was REALLY wrong. They diagnosed reflux, but I couldn't get gaviscon into her. I spoke to the doctor on the Monday and he prescribed carobel - again, impossible in a 5 week old breastfed baby - she gagged on it. I spoke to the health visitor then, who referred me to a breastfeeding specialist and a breastfeeding support group, and we ascertained it wasn't reflux, or silent reflux, but colic. And then we tried everything to make it easier on all 3 of us until it passed.
I found it was lesser if she'd had a good sleep in the afternoon, 2-2.5 hours on me, or on my mum so she felt skin, warmth etc.
Various things helped press the pause-button while it was in progress, over the shoulder, Tiger pose, classical music, the noise of a fan, walking in the pram, driving, going outside into the cooler night air, being naked, swinging DD in her carseat, gently bouncing her in the bouncer, white noise, the mobile over the cot, walking around, darkness, a bright light, sitting on the toilet with her while DH took a shower, or just with the shower running. omg I tried EVERYTHING.
I didn't find infacol any use, and while DD did far in the middle of the crying, I think that was coincidental, a consequence of all the exertion. I don't believe it was bubbles in her tummy.
It was heartbreaking hearing her cries echo off my breast as I tried to put her on. Don't stop breastfeeding, I'm sure you're doing great and I'm sure your child is getting enough - weight gain okay? Plenty of wet nappies etc?
We found that in order to "break the spell" we had to get her to sleep before it was due to happen or as soon as possible onto it - by whatever means possible. This is excruciating if you're used to feeding to sleep, but it had to happen for us. DH might drive and I'd sit in the back with her, we'd have BBC world service or classical music on the radio. If she'd sleep for 30 mins, she'd "reset" and take a big feed and calm down. If not, rinse, repeat until she's calm.
It took its toll on us, and I read an article about parents suffering PTSD afterwards! Make sure you're taking turns, and taking a break, I did the bulk of it as DH really couldn't cope and we ended up fighting or silent treatment when DD had finally gone back to sleep.
If I needed a few minutes to myself, DH would hold her with his earphones on, or I'd lay her safely in the cot, pee, have a drink of water (build up the milk for when the craziness stops), go outside to cool down etc. I'd hold her and put the telly on and read the subtitles to concentrate on something else and stay calm, all the while shhhhhing and swaying and rocking and loving her, even though it was deafening and heartbreaking! Don't be ashamed to walk away for a minute - the crying will happen regardless. I would never let her cry it out, but 2 mins will save your sanity. And remember while you're holding your sweaty, bawling baby, there will be an end to it this evening - even it it's 4 hours away, it won't go on forever tonight or indefinitely - she will sleep later, and she'll grow out of it, and soon you'll be on to the challenges of teething or something else!
PM me if you want to chat