Welcome to HCM.
Your LMP was on Aug 12th and you did sex on Aug 28th around ovulation period or fertile zone.
You got very little pink bleeding on 3rd Sept and also in 20th with abdominal cramping.
It may be due to early implantation
or Threatened type abortion
(which is recoverable) or may be with hormonal
Do immediate home pregnancy
test for hcg to rule out pregnancy and if it comes positive,do a USG to get details about fetal profile.Always consult to your doctor.
by deep breathing and yoga as it may cause hormonal imbalance and irregular period with spotting.Do light exercise if pregnancy test is negative.