It appears your daughter is suffering from anxiety - whether it be separation or generalized or social is irrelevant. I suspect the health issues you have stated are all the result of untreated anxiety. If anxiety is the issue, I assure you that your daughter will not outgrow it nor will it go away. Untreated anxiety can ruin a life. By the way, anxiety is highly treatable and a very common mental health issue.
The first thing you should do is contact your family physician and ask for a referral to a medical specialist with experience in anxiety disorders. It appears the doctors you have been "seeing" are not experienced in this mental health disorder. Very young children and adults respond to treatment quickly; unfortunately teenagers are often the most difficult to treat (don't know why - but that is no reason to wait). If you would like more information on the internet, I might suggest you google the term "anxiety disorders" or "anxiety in children" or "school refusal" to educate yourself about this issue. Please call your physician as soon as possible as this disorder will only get worse. We've been there - I wish you the best ...
It is possible that the Meds she is on are having side effects you could ask her Doctor if this may be the case, what med is she on for anxiety?13 is a hormonal kind of age and she probably needs a lot of positive attention and affection, what is she like at school does she have problems there or is it only at home? May be good to try not to feed into her behavior as it may be a way of her getting more attention, focus on her positive side , does she have outside activities and sports , if Dad is around get him involved playing games with her,and doing more physical activities .