Decidual bleeding - negative HPT ???

Hi,

I was wondering if someone could help me, i did a hpt about 7days ago and it gave me a very faint positive line..i did 3 more after that the next day with the same result...a very faint positive.i was due for my period 5days ago and i started to bleed with some cramping...it was very light and i was told by my gp it could be decidual bleeding.I stopped bleeding yesterday and did a hpt this morning and received a negative result..i dont know what is happening...how long do i have to wait before i can do a test again...did i get a negative because of the bleeding??...but it''s stopped now so surely that could not of effected the result??..can anyone shed any light on this??...im really worried that im not prego anymore