Smudgered well done for getting out and for emailing the Samaritans too.
I haven't 'met' you before but it may well be that you aren't happy because of your relationship with your dh which seems strained at the very least. Having small children/babies puts a real strain on marriages, and if there isn't a lot of give and take it can be incredibly difficult.
However you are also depressed, you said, which is an illness, a chemical imbalance which means that even if your dh were perfect, you would still not feel happy. Only medication and other practical steps will help. (I do know. I had horrific PND with both of my boys, and battled on for months/years)
Ask your hv/gp tomorrow to review your meds. They can take longer to kick in, but I believe that you should be seeing some difference. Maybe they can change the dosage?
Something I also found really helpful was to have a timetable of possible activities to get me and the boys through each day too. They weren't big things - we couldn't always manage a lot - but having a list of things to do each day (I kept it on the computer, on a spreadsheet) and then ticking them off, helped me through long hours: eg:
Get up
Breakfast
Get dressed
Wash up
Water play for kids (ie a bowl of water and some toys, on the bathroom floor)
Telly time
Walk to park/shop
Lunch
Wash up/Lego tower building
Tidy up lego
TV time?
Mid afternoon sleep
More Telly time
Supper
Bath
Stories
Bed
There can be other things to add, as the kids get older/have different favourite games. I found it helped a lot, having the toys out of the way, then going to get something out - plastic animals/paint/ cars/play dough etc - for half an hour, then putting them away again, rather than letting the kids wander amongst all of the toys and not choose anything.
The other thing that kept me sane was MN! Do keep on posting!