I had two MMC last year, one at 12 weeks and one at 9 weeks.
Firstly I'm so sorry you've been through this, it is a really awful thing to experience.
Third time lucky for me, I'm 24 weeks pregnant now and I felt completely the same as you in the first trimester. The difficulty with having a MMC at 12 weeks is you mentally have to get past that 12 week point before you can relax a bit and at 5 weeks it feels like forever away.
Please know what you are feeling is very common and totally expected after a loss, you're not alone and there's a huge amount of support from other ladies who have been through this.
At 5 weeks, I didn't really have many symptoms, I found they really kicked in around 7 weeks. There was definitely days where I felt completely fine and panicked and then a few days later it would all come back again. I don't think symptom spotting is accurate anyway as I still had morning sickness and sore breasts after miscarrying both times.
I bought a book called Pregnancy After Loss, I would really recommend you get a copy. Also, are you able to get any sort of talking therapy? It is really common to have PTSD after a miscarriage, so talking through the trauma with a professional can really help you process it.
With each milestone it does get easier. You'll get past the point of your miscarriage, then have your 12 week scan, then you will start to feel baby moving, then you get your 20 week scan and you will find yourself starting to relax a little at each of these stages. I have only just felt able to start telling people I'm pregnant so I really understand the fear and worry!
The first trimesters is truly shit and I wish I could say to you 'don't worry' and it would help, but honestly you're going to worry and panic about everything but you need to practice some techniques to relax like meditation, mindfulness, breathing or yoga to get you through to your 12 week scan. Do the best you can for the things you can control - eating, sleeping, taking your vitamins, exercising/going for walks. The rest is out of your hands and you just need to trust your body and hope for the best.
The other thing that helps some ladies is private scans, for me personally it just gave me an extra thing to worry about, but see how you feel.
Really really good luck, keep putting one foot in front of the other - you've got this!!