Pumble you are undoubtedly really stressed. I know, I've been there as an 'old' mother with no support, and recently following an operation. Above anything else, what you need is help.
My dd cried every night from about 6pm until about 1am until she was nearly 12 weeks old. Then, somehow we both got the knack of feeding, and she never cried in the evening again, and used to sleep from a feed about 6pm until another one at 10pm. Infacol was useless, and absolutely no-one from my ante-natal group found it any help at all. Later the empties were brilliant as, once sterilised, I used to fill them up with gripe water, and give 1 full squirt - about a teaspoon - down dd's throat before starting a feed.
Another thing I read was a brilliant article in Mother + Baby, which came too late for me. It was about the fact that you need sleep to produce the hormone that causes the production of the richer breastmilk that is more satisfying, rather than the thirst-quenching lighter sort. If you don't get enough sleep, the sweeter lighter milk can give little babies stomach ache. It made sense to me that at 2am after even an hour of sleep if I was lying squashing a breast, I could soak the bottom sheet on our bed. Even an hour's sleep in the afternoon - especially if it's curled up with dd1 for a cuddle would help - that's assuming she still has a sleep in the daytime.
At 4 weeks, according to the recommendations that were current when dd was a baby, gripe water can be given after 4 weeks. I used Boots - and gained loads of points on my advantage card in the process, as with sudocrem etc, even if in darker moments, rather than buying make-up to give me a boost, I bought Twirls instead.
Please also think of getting your thyroid checked, too. The changes in your body during pregnancy can lead to thyroid problems (as well as other auto-immune disorders like diabetes) the symtoms of which can be very similar to depression - ie weight gain or the inability to lose weight, crushing bone-numbing tiredness etc a bit like the week after flu feeling crossed with being hit by a bus, if that makes sense.