I have what I consider to be a "high needs baby" and let me tell you, it does get better!! Obviously it is important to rule out a medical condition, but unfortunately some babies are just super fussy. I found it so hard, but was also lucky that she slept well at night, so at least that was some respite.
Things started to improve around 14 weeks or so for us. Slowly at first, so I was able to put her down for 5 minutes at a time. Then gradually over the next few weeks I found her attention could be held for 10 minutes at a time. The times I have noticed improvements have been:
When she became aware of toys and could hold them and put them in her mouth.
When she could hold her head steady and look around whilst being carried.
When she could sit with support.
She is now just over 5 months, and whilst she is still not the most placid baby (my friends' babies always show is up by sitting on their mums' laps for a whole entire lunch!), we can just about make it through a baby group without a meltdown. I try and time things so she has a feed just before we go out, or as soon as we arrive at a group, and she is usually fairly calm just after having a feed.
It is so hard, but your baby doesn't hate you and you aren't a bad mum. Do confide in someone about how low you are feeling regarding it all. You need someone to watch out for you and make sure you don't get too overwhelmed by it all. And never feel guilty for handing the baby over to someone and getting away from it all. Similarly, if the crying is too much in the daytime, put him in his cot and leave the room for a few minutes. He will be fine.
Good luck, it does improve!