I've been feeling more tired and have some flashes of light. when should i see the doctor?

Soon: Feeling tired and seeing flashes may or may not be related. Anytime you see new flashes, you should be seen by an ophthalmologist within a couple of days.

As soon as possible: While tiredness is usually not associated with flashes of light, it can be associated with lightheadedness (which can sometimes give the appearance that you are looking through a glass of soda). Flashes of light tend to imply a retinal issue, and although the condition is benign the vasst majority of the time, there is a risk that something more serious is happening. See an eye doc immediately.