Hi 1is!
I'm an old hand at the PND game (my youngest is 6 now). I was on a M&B unit briefly with dd1, depressed with ds, probably most depressed with dd2 but better at hiding it by then.
You probably need a bit of help right now, whether that is from your HV, or GP, or family and friends. IME, 6 weeks is when the real tiredness/sleep deprivation kicks in! And if you are under the weather mentally as well, then it is much much worse.
I see StrawberrySam says she is strugling with severe PND but not taking Ads cos of BF. That's some bad advice there - I took antidepressants all the time I bf all my babies, apart form the last 4 months with dd2. I took them right through the pg of ds and dd2. There are some pills out there which are really helpful and safe (well, unless it is the pills which have made my kids so funny, sparky, clever, artistic, musical and great fun to be around).
I know a lot of people are worried about antidepressants. You might have good reason for this (there is one I will never take again as it made me very ill) but there isn't a lot of difference with injecting insulin for diabetes or taking thyroxin - it is correcting a chemical imbalance - in your case and mine in the brain - and it most often works!
There are other helps available however - Homestart can help you if they are in your area, just giving you a litle break. There is help from the GP in terms of CBT for depression etc which is useful but can take a while due to waiting lists. You shoudl ask for help soon-ish to get it before the summer.
I remember sitting weeping over my 6 week old and my dh realising that it shouldn't be this way (and he's a GP!), I shoudl be enjoying my baby and making the most of it. Sadly, I have very few memories of the first months of any of my children's lives as I was so sunk in depression it has all been blotted out. It would be awful if this happened to you as well.
Congratulations on having a lovely dd. I think one of the things which made me seek help (well, for me, apart from the threat of being sectioned as I was that ill!!!) was that girls who grow up with a depressed mother, even from the earliest days, are more likely to be depressed themslves in the future, esp PND. I look at my 10yo and 6yo dds and think NO! it stops here - I will not do any less than my best to stop them suffering what I have. ANd I don't liek taking tablets much - but if it gives my dds a better chance of being healthy, happy mums themselves, then I will do whatever it takes.