I was told to take all my antibiotics for a sinus infection i took them for 2 weeks and forgot to take them for 3 weeks. do i start taking them again?

Probably not: Taking them now would be like taking 2 subeffective courses - you should actually see your doctor if your symptoms are not fully resolved and if they return do not just start your leftovers.

Stopped Antibiotics: Go back to your doctor to get a second, different antibiotic. The "bugs" change during the course of an infection. A antibiotic should be taken for the full course. If symptoms persist, think "new antibiotic" or "another diagnosis"?.