So confused the 1st time I had covid nothing was mentioned about not being able to retest before 90days! This time the NHS have said I can't retest before 90 days as it could still be in my system. I'm high risk and work in a school......its riff at the moment I've only been back 1 week and worried if I get it again (still mask wearing, sanitising every second) How will I know I'm infectious and where do you stand ref: isolating. Can't find any information.