Thanks for query,
As your last period was on June 24 & you started spotting on 7th July followed by heavy bleeding doesn't indicate any fertilisation process.
This is purely a dysfunctional uterine bleeding
due to hormonal
Hormonal imbalance can be occur due to tension ,Anxiety
,Late working hours,Shift duty or due to ovarian diseases.
So consult your gynec he will prescribe you medicines to stop flow after test results.