Ugh, I remember 3 weeks old (NOT with fondness, I'm sorry to say) - it was really, really challenging for us. I drove myself crazy trying to figure out why she was crying. It can be so many things, or really nothing at all... it's tough to figure out! So, I would do the research you can, ask for help and advice, but also try to bear in mind: 1. it will pass! at some point, things will get a lot easier and 2. everyone has a different experience, so take a deep breath when you're trying to run through the list and figure out what it is.
That said, many babies get extra fussy in the evenings before bed, and my daughter was no different (she still gets fussy but doesn't lose it as much - things got WAY better around 5/6 weeks - she's now 3 months). It was hard to get used to, because the best thing you can do (if swaddling, shooshing, nursing, etc aren't working) is walk the baby, and I was always too exhausted to do that! Can you put her in a carrier and have your husband walk her when she's so upset so you can get a break?
For us, it turned out that my overabundant milk supply was leading the poor thing to get too much foremilk (there's a great article here about foremilk vs. hindmilk and oversupply:
http://www.llli.org/FAQ/foremilk.html ), which made her very gassy and constantly hungry. So she would try to eat, get a WOOSh of milk that was hard for her to handle, get temporarily full with light, gas-inducing milk, get uncomfortable because of the gas, and want to nurse again, which made her more uncomfortable. I think she would finally get so tired that she would quiet down and fall asleep, but then start squirming with gas pains again from 4 or 5 am on. phew! She also threw up a lot (not spit up, huge huge stomach fulls of milk) because she was just getting too much.
Anyway, that was my experience and block feeding and taking sage tincture helped a lot. But every baby and mom is different. I hope you can get some relief soon, but no matter what it is, most baby issues are digestion related (in my opinion) and start to get easier after 6 weeks. Good luck!