Hi OP, sorry to hear you are going through such a tough time :( I can relate because in the first trimester I also suffered from very low mood and anxiety - it was worst around weeks 8-11 I think... from about week 12 it got better. First trimester is extremely tough on your body - you're not only growing an essentially complete mini baby but also a placenta. It's a huge strain and the hormones will wreak havoc for many.
I always suffered from quite bad PMS - low mood, emotional etc - so it made sense to me that during pregnancy I might also have similar or worse hormonal symptoms. Have faith it's your body doing its thing and that you will come through it - it almost definitely won't last the full pregnancy. But there are ways to cope even if the hormonal moods continue.
Counselling could help (personally I have never found the free NHS service good but have found private psychotherapists good) and there is also a free mental health service linked to pregnancy too. Talk to your midwife about it. Anything is better than nothing!
Mindfulness practices like meditation and exercise (even just walking, but prenatal yoga as well) can also really help. How is your appetite and nausea? Can you eat nutritiously? If not, don't worry, it will pass - I had vomiting and nausea till week 16 but now I feel amazing (week 21). Jut eat what you can and make sure you're eating something at least.
Talk to someone. A close friend can offer amazing perspective.
Nutrition and gut health can help with mood so invest in some good probiotics, eat some live yoghurt, plenty of fibre, omega 3 such as avocados and fish, eat veg if it doesn't make you barf, and lots of fruit.
I have had body image issues in the past so understand it can be a scary time when you have this hanging over you. Remember, you will lose the weight you gain, especially if you breastfeed. You also may not gain that much. I don't think I've gained anything yet aside from the obvious baby bump (don't have scales tho, but going off how I look and feel). Remind yourself that the changes your body goes through are temporary and giving life to your baby. It is an amazing thing.
Lastly if you are terrified of birth - I highly recommend two things. 1. The Positive Birth Book by Milli Hill (it's incredible, so informative, relatable, funny - I feel so much more confident) and the Positive Birth Company Hypnobirthing Course (again, so useful, really explains what happens during birth with your body and prepares you with amazing techniques to handle the process).
Good luck and happy to chat on DM if you like, I hope you feel better x