I've never had a baby from being a newborn, we adopted both our DDs from age 1. Looking back now, I had what's known as post adoption depression, feeling flat after the stress of the application process and then the transition of the child from foster care to permanency.
In the first weeks after DD2 came to us, we didn't bond straightaway. I was constantly crying and thinking it would never happen. She wouldn't even let me feed her her bottle. I convinced myself that we'd made a mistake and should give up. My DH tried to understand, but he didn't have that problem, as DD2 bonded with him immediately.
What really helped me was getting away one day and having a cup of tea in the Morrisons cafe. Just having some time on my own. It didn't immediately get better, but I never again wanted to throw in the towel. Then one early morning (she didn't sleep well, so it was 4:30, I think), I suddenly found myself holding her and giving her her bottle of milk, and she was no longer resisting. It was such a special moment.
It was exhausting, though. She was very clingy with me when DH was in work. I couldn't even leave her with my DM/ a friend so that I could go to the toilet. She would scream her head off. She would only let DH or me change her nappy. In the end, in desperation I put her into nursery for two mornings a week. The change was amazing. She cried when I left her the first few times, but she was all right after that. She's 6 now and we have an amazing bond now, but she can still be standoffish and with other adults and with DD1 (9), and has very firm boundaries.
It was one of the hardest times in my life. But what I take from it, and I think may help you, is that getting away on your own, even if only for a short while, can really help. Because sleep deprivation does things to your head and makes it feel like the walls are closing in on you. Maybe you could leave the baby with your mum for a few hours so you can catch up on your sleep or go for some retail therapy?
Meantime, hope it's gone well with the GP. Be kind to yourself. And your mum and DP need to be more supportive. 
