Your question is a classic example of the chicken and egg question. Which came first the anxiety or the physical symptoms? There is a constant subtle interplay taking place between mind and body throughout the day therefore the answer to your question is not straightforward. Given the fact that you have a previous history of significant anxiety disorder and are currently in the final trimester of pregnancy it is more likely that your symptoms are anxiety related. Pregnancy can be an anxious time and anxiety levels can rise as the expected date of delivery draws closer. Make sure that you attend your antenatal classes because you are usually instructed in relaxation techniques in those classes. Relaxation exercises would be a practical help to you in your current situation.