Advice

ok my question is i started what i thought to be an early period on july 10 and it lasted until the 29th for some reason which has never happened before i always have heavy 7-9 day periods this one lasted weeks but never got as heavy as a normal period.On the 2nd of August it started again only it was light like spotting and stopped on the 5th i had a blood pg test done at the er on the 2nd which came back negative but if it was implantation bleeding would it come back positive or was it to early? And any ideas on what i should go by for caculating my period should i go by the 10th of july or the second of August as my last period im confused