When to take a hpt

So last month in the beginning of May I had my period(lighter than usual and didn't last as long) but I didn't think much of it. Then two weeks or so later I start spotting (lasted roughly two days was a dark brown) so now I've been waiti for my period for this month(June) and it has yet to come. AF is roughly four days late and I took a hpt just now but it was negative. Could I still possibly be pregnant? When should I test if so to get the best/accurate result and should I be worried if my period doesn't show