Hi OP, firstly, congratulations.
You sound like you are very overwhelmed at the moment and you have had loads of good advice already.
I just wanted to add a few comments.
It absolutely does get better, he will stop crying, he will sleep more and you will begin to understand what he is trying to tell you. But right now you are in the thick of it, and it won't all happen overnight, so please be kind to yourself and try and take things day by day.
He is 14 weeks old, barely knows he has been born and half the time might not know why he is crying himself. Re the silent reflux, it is a thing and if you have noticed he is much happier upright it could be an issue. Quite often babies outgrow this around 3 or 4 months. Also, if he is on gaviscon this can make him constipated so it is a balancing act. If he is opening his bowels regularly though then I wouldn't also be giving the lactulose as it isn't required.
Apart from the possible silent reflux, is he showing any signs of cmpa? Explosive smelly poos, rashes, vomiting, poor weight gain? True cmpa in breastfed babies is actually very rare and if you have omitted all dairy from your diet and aren't seeing any changes then it probably isn't cmpa.
How you feed your baby is a very personal thing. You have done an amazing job breastfeeding for the past 14 weeks. If you do choose to introduce formula you can also choose to combi feed and continue to breastfeeding as well if you wish, it doesn'thavetobeone or the other. If you are concerned re reflux there are anti reflux formulas but you wouldn't give the gaviscon alongside it as it is already thickened to prevent the reflux.
As for when he will sleep better, how long is a piece of string? Some babies do sleep through early, some don't. Being calm and consistent helps, but at 14 weeks and breastfed I really wouldn't be expecting it yet. There are tips for gentle sleep training for when he is older, but try not to overly worry about this for now. But I would certainly be trying to settle him in a moses or next to me so you can take your medication.
I know you say meds haven't helped in the past, but taking them alongside your therapy may help. I also think you should speak to your health visitor to see if there are any parenting courses or groups specifically for parents who feel they are struggling to bond or understand their baby. For what it's worth, I think the fact you are posting, and trying so hard to understand him, shows what a loving caring mother you are, even if you can't feel it at the moment.
Yes, your life has changed, you obviously know this. But he won't be this tiny for long. Everything is a phase, you crack one and they move onto the next. But also, every phase comes with new opportunities. He will grow so quick, he will soon settle in nursery, go to school, be big enough to jump on a plane and go on adventures with you. Or be left with a babysitter while you have your own. So while it feels like this is your life forever now, know that there is so much more to look forward to unthe future for you both 💐