Welcome to HCM.
Your last LMP was on 1st July and had sex on 14th and 16th.After that you had been bleeding lightly for 7 days.
It is probably due to early implantation
bleeding and your pregnancy test is negative.
I suggest you to do a USG lower abdomen to evaluate underlying pathology. Also do some hormonal study like thyroid profile,LH/FSH, Serum estrogen & Progesterone
along with PPBS,blood group
& typing for both etc.
Then consult with your doctor according to test result obtained.
Take healthy diet with vit-E supplements,Folic acid
& Calcium.Avoid stress and proper rest.