please help me):

so my last period was the 18th of July it lasted 10 days idk why was that ): I was worried and I was supposd to get my period the 15th of August it's been 7 days . I took a preg test and it came out negative. when my period came on the 18 of July I took BC and the 19th I took BC but then stopped . is that the reason why my period is late ?