Hi i tested positive for covid on 15 december. completed my quarantine was feeling fine just had a residual cough, intermittent diarrhoea and fatigue. my fever is now back this evening 38.1c with myalgia. what could be the cause? should i reisolate?

Hard to say: Definitely sounds possible that you could have a relapse of Covid, but also if you have any other symptoms like pain with urination, cough with phlegm, or other symptoms you might have a secondary infection like urinary tract or pneumonia. I would recommend isolation yes, & at least a phone or video Dr consult if breathing issues or other new symptoms. So difficult to be sure these days!