Well, of course you really need to be carefully assessed by a doctor but since you have asked for an opinion on here, I would say it is classic signs of a chronic anxiety state. I think you may not have properly got over the miscarriage and you might be mildly depressed, too. Stress, anxiety and depression can lower your immune system and that is why you may be getting repeated colds and sore throats. Feeling your heart beat or having pains in your chest are also classic signs.
Make an appointment to see your doctor and go through all of this with him/her. I would write a list of all your symptoms and that way you will miss nothing and, should you become a little upset in the doctor's office from talking about your problems, then you can just hand over the list.
You should also try to keep a journal of your symptoms, day by day, noting whether or not anything seems to bring them on. Take this with you to the doctor, too.
The chances are you will be given some relaxation tips and perhaps referred for some counselling. I know it feels like you will never be free of this cycle of ill health and stress, but it will go eventually, believe me.
