Crippling health anxiety

For a year and a half now I’ve been suffering with awful health anxiety, I literally cannot stop thinking about what might be wrong with me. And being a 2nd year student nurse i just feel ridiculous. My anxiety stems around infections diseases especially STI’s and HIV. I’ve been with my partner for 18 months and everything I’ve been tested for has come back negative. I have been 2 weeks late ringing the doctor for results due to being petrified of what they might be, but at the same time have been into more walk in centres than I can count. I’ve also had CBT because my health anxiety was causing daily panic attacks. which helped for a bit but it always seems to come back with a vengeance.
Has anyone else experienced this and have any advice?