breaking point

Hello. I'm wondering if anyone has any advice. I have major depressive disorder and I am really struggling to be a good mum.( I have 4 kids..16..13..4.5...& 18 mths) I have just changed my medication but not sure if it's working.
I feel like I'm really letting my kids down by not doing things with them but I just can't get passed whatever is holding me back . I feel like I just don't want to be here anymore as I'm ruining their lives slowly I have thought of suicide but it's not something I could do to those left behind. I have had counselling in the past which got me throught some really rough times but then my counsellor left and I basically got lost in the system.
I'm sorry for rambling but it's hard to keep short :)
TIA