It sounds like you are suffering very badly from anxiety. As everyone else has said, you should speak to your midwife or your GP as soon as possible. You are right, you are making yourself ill, but it is not your fault.
I know that nothing will reassure you at this stage but I thought it might take the edge off to share my experience. I also suffered from (much less severe) anxiety after falling pregnant after a MMC last year. I thought the 12 week scan would put my mind at rest but in all honesty I have continued to experience niggling feelings of anxiety throughout the pregnancy, and I am almost 35 weeks now. He was a late mover (only now settling into a routine of movement and although these movements are strong he just rolls about, he very rarely kicks) and I only really started to calm down after these movements became regular, which I'd say was not until 30 weeks or so...
One thing I remember very vividly is a period when I felt I should have a bump, or the beginnings of a bump - maybe 14 weeks? - when my belly looked completely flat in the mornings. Even at my 20 week scan there wasn't much showing and it was 25 weeks plus before people started to comment on my bump. I remember asking my midwife if it was normal for there to be no bump and she just smiled and said not to worry - I would have one before I knew it. Now I can barely move for it :)
IMO the early part of the 2nd trimester was when I felt the least pregnant. The earlier, stronger symptoms start to clear up but the baby isn't moving yet and you can get a burst of energy back which makes you doubt there is even a baby in there.
You are losing weight due to stress and that is making the feeling worse in your case. Try - and I know it is nearly impossible - to cling to the memory of the scan, and seeing your healthy baby on the screen. In the weeks that follow you will hear his / hear heartbeat at every midwife appointment which I found very reassuring.
A little later on you could look into getting a fetal doppler which you can use to listen to your baby's heartbeat at home. I've heard a lot of people with anxiety issues find these reassuring although I haven't used one myself.
Hope this helps a little and you manage to speak to your midwife / GP very soon x