Dee I am so sorry to hear that things are tough for you, it must be so hard when you feel so isolated and alone. I would say that if your mum is able to come and help then let her because by the sounds of it you need some rest. I am sorry to say this but your DF sounds like he is being incredibly selfish, has he even considered how it must be for you to be dealing with it all day?
I wish there was more that I could do to help, I guess the only advice I have is that if you know something is not right go back to your GP and INSIST that they find you some help, if not why not try ringing a counselling service and see if they cant put you in touch with someone. I guess basically it comes down to go with your gut, and just keep pushing untill someone listens.
Please consider asking your mum for some help, maybe she can go to some appointments with you to back you up and try and get you some help!
Make sure you take care of you, even if that means handing Lachlan over to your Df when he gets home and going for a walk around the block!