I'm not a Mum....so, I hope you don't mind me mentioning...everyone is different.
I have a few mothers working with/for me. One of our para-legals started maternity leave in 2005 - the intention was to stay at home with her baby for 12-18 months.
After 4 months she called our PR person...she HAD to come back to work. It wasn't working for her - she felt bored, isolated and unhappy.
We suggested she try 2 days a week - it worked - she ended up being a happy para-legal and a happy Mum.
I suppose what I'm saying is...if the current "arrangement" isn't working for you - rather than stay unhappy - look for something that might make things better for you and your child - perhaps, utilize a play group a couple of mornings a week or ask a friend or relative to take your baby for a few hours.
It seems to me there is often pressure to be the "perfect Mum"...be quiet, don't complain - when Mum's finally ask for help it's usually a desperate last measure.
I can't see anything wrong with someone saying they're not happy and doing something about it...some women love being SAHM's - others need to work or need some other outlet...
I know our para-legal was criticized by her MIL & others but, sometimes you have to develop a thick skin and do what you think is right for you and your child...
Good luck everyone...