Hello @Alli1002, welcome to the forums and thank you for sharing your story. It sounds like you are in a really difficult situation right now. I can't imagine how frustrating it must be to go to the doctors for some support and to not get the support you need. Have you had a chance to go back to the GP to let them know that the exercises did not work? They may be able to suggest that you try something else. Or you could also try to see a different GP to get their opinion on how you can help your daughter.
Has your daughter spoken to you about why she has been trouble falling asleep? Could it be that something is on her mind and she is not able to "switch off"? This could be an important factor in how you could treat her sleeping difficulties.
I am sorry to hear that this has been impacting on your marriage. It is really important that you are also looking after yourself in these times. Have you had a chance to talk to a counsellor or psychologist about your daughter's sleeping difficulties and how this is impacting you? Some free helplines that you can call are Parentline and KidsHelpline. We also offer a free professional service that provides one on one support. You can read more about it here.
Please feel welcome to keep us updated. 
