If you went to the doc and everything checked out it is very likely anxiety. Anxiety can make your body do a lot of things, including chest pain. It is your body reacting to the stress. All the symptoms you have listed can be from anxiety. The best thing to do is to work with your therapist on ways to overcome it when it happens. Try closing your eyes and taking deep breaths.
Are you still anorexic? Because that can cause nutritional deficiencies that can make your muscles hurt -- such as a lack of magnesium, for example. A lot of times doctors don't test for this type of thing. So have you started eating again, and do you eat green leafy vegetables? Do you drink enough to stay hydrated? It could be anxiety, but it could be muscles pain as well. I don't think it's the heart.
If all your checkups turn out to be negative from possible diseases then I think it's safe to assume that what you are suffering from is indeed anxiety. You and your therapist should work on this. It's fairly common for people with eating disorders to develop anxiety and chest pains can be a symptom. Start with therapy treatment and eliminate your worries. I do hope you get well soon.