Hi OP,
I'm sorry you're having such a rough time at the moment and that you lost someone so dear to you.
I think it's all of the above...pregnancy screws with your head and body, grief is probably the most physically and emotionally draining thing you can go through then depression on top is only going to amplify all those negative feelings.
First things first, is remember you will come out the other side but just accepting this is how you feel right is probably the first step rather than fighting it. You have very genuine reasons to be feeling how you're feeling.
I loss my Nan on 22 Dec 2018, 8 months before I fell pregnant - she was probably the person I was most close to. Even now, I'm struggling with my grief and will do for a long time. I now find my anxiety is through the roof - I've been off meds for 7 years but some days feel like I'm right back at the start when I was at my very worst.
I'm not sure about medications - I know that they don't like switching them when you're pregnant. Are you taking any supplements I.e. vitamin D, B12 etc I found if my Vit d and b12 get low, I get very lethargic and then that effects my mood immensely.
I've also found grief groups helpful - I started going to one near my work called the new normal. Even just listening to other people's stories, experiences and ways of coping really helped. Maybe have a look what's in your area? I'm presuming that with your mums illness there was a palliative care team and they usually have support in place for relatives as well, so may be worth contacting them?
I spoke to my midwife and explained that I'm struggling both physically and mentally - there's been steps put in place now so that if I get any worse I can ring the perinatal team to get support now and when the baby is born.
Talk to the people that care about you is the biggie - I very much tried to deal with my grief/anxieties on my own and then would break down on the regular with my partner. All my friends thought I was managing and were quite shocked when I explained how bad I was feeling. I don't know whether that's something you've done but don't shy away from being emotional or honest with other people. We all lose someone we love eventually and it's the one thing that a lot of us can relate with.
Sorry for the long post! Xxxx