You may not have the power to change your situation completely, but you have the power to change your negative thought patterns and feelings about yourself. One way is improving how YOU treat yourself. PAMPER yourself, this maybe through exercise, going for walks, having your own mini facial/self-care routine in the evening, anything that makes you feel good. By looking after yourself you are more likely to do an amazing job looking after your baby.
There is no need to let your ego get in the way of asking for help. Speak to your family or friends every day, don't isolate yourself. Ask a family member to help out when the baby arrives, it maybe with babysitting so you can get a nap or break, or it may be help with chores. Attend baby groups, meet new Mums, share your worries. Just don't bottle your feelings in. You are more than likely to meet people who have similar worries and experiences, and it will make you feel better knowing you are NOT ALONE in how you are feeling/what you are experiencing.
You may think speaking to your GP is a waste of time or nobody will do anything, but it is important to know there is so much support including midwives and health visitors, along with your GP who can be more intensively involved in your care if you are vulnerable/depressed. You can get access to counselling and even medication if needed. For further information on mental health support available online please check out- https://centreforearlychildhood.org/find-help-and-resources
