I tested positive for covid 3 days ago, ive been running a low grade fever for 4 days. how long should i except this fever to last?

The fever is not the enemy, it is just an indicator of ongoing inflammatory process most of the time it has no lasting effect. The duration depends on how quickly your body contains the infection. You could speed that up by adequate rest and nutrition to build up your immunity. If you have underlying illness like diabetes, hypertension, HIV, liver or kidney disease you qualify to be on medication.