Welcome to HCM.
You did unprotected intercourse
1 wk after your period i.e. near about on 22nd Sept (LMP 15th Sept). As your period is not regular,then chance of pregnancy
Next you did again unprotected intercourse with an other bf on 12th Oct i.e. 1 day before period date.
Here pregnancy chance is minimal.
You repeat hcg
test with urine or blood and do a USG scan to rule out conception or other pathology.
If conception is there,do a DNA test if you want to carry this and confirm who is responsible for pregnancy.Always consult with your gynecologist.