Stress and feeling of impending doom.

I am under a lot of stress these days. I know many many people are but I just feel extremely vulnerable and sensitive. Feel numbness in my left leg (calf area) sometimes, though no pain. I also get this periodic back head pain for which doctor treated me with anxiety medicines last year but they have returned. Not taking any medicine now. I also get gastrointestinal problems too easily these days. In short, just feel unwell both physically as well as mentally and all the time my mind keeps racing to as if I might have some serious disease and like I am gonna die soon. I try to keep myself active, also engage in multiple things and have even started studying for an exam but my studies, job, life all are getting impacted due to these thoughts. What should I do?