I'm a stay at home mum of twins now 2yrs 7mths who are doing just fine. I have had pretty severe depression since they were 10mths old caused mainly by being bullied in my last job - the one I had whilst pregnant. I have struggled massively with confidence - that I am able to bring up two healthy children. I fear the judgement of others if they see me panicking or anxious (I have social anxiety as well as depression) or depressed. I have help from a mother's help who comes to playgroups with me and helps during the day, at bathtime etc - twice a week now. Other mothers often snub me thinking I'm a posh mum who doesn't want to do it herself. Yet because of the stigma it's hard to be honest. MIL seems to think I'm totally good for nothing as need so much help with kids. Sick and tired of being judged!
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Mental health
There is nothing wrong with getting help so ignore your mil. I am lucky as I have family that help with my dc when things get too much but it has taken me a long time to let them help. I too have suffered with depression and felt that I needed to prove I could do it on my own so its been quite a big step to take the help.
It does seem hard to be honest about depression to me when in reality so many of us suffer with it. I have found some good friends who I can talk to and it gets easier with time.
Do you ever chat with other mums at playgroup? Maybe if there were 1 or 2 you could get to know a bit better then you could try and explain a bit of your situation, just the bits you are comfortable with.
You sound as if you are coping really well, you say your dc are doing fine and you go out to playgroup so thats really good.
Stay positive and try not to worry too much about what other people think. 
i agreewith the above poster, that you should ignore what other people think. as long as YOU know that are doing well and YOU know why you need the extra help who cares what other people think.in fact, you should see it as a sign of strength that you are looking out for what is best for your kids, and getting the help you need to ensure they get everything. its far better to get help to go to a playgroup than to not go at all because of the lack of help.
also, mothers in law can make daughters in law feel bad about lots of things, it doesn'tmean youre doing anything wrong.
i think kitakat also has a good idea, that you could get to know some of the others better,1 or 2 of them,then you could confide in them.
are you doing anything to get help for your depression, ie therapy, or anything else?
on a completely separate note i'mnew to mumsnet and im finding it really interesting and at times frustrating which threads get the most interest. here is a thread from someone who really needs some encouragement and support and there's only been one reply. yet the threads on things like 'hooter hiders' and 'was Denise Van Outen right or wrong to give up breastfeeding' have so many responses its silly. 
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