Hi,
Welcome to Healthcare Magic Forum.
I have gone through your Query & I really appreciate your concern about the problem you are facing.
Brief Answer :
No Need to worry. You are not pregnant.
Detailed Answer :
As a physician I would like to tell you that as you have said in history, you got your periods after your sexual encounter, so you are 100% not pregnant.
Also I would like to elaborate here that there could be various reasons for changes in characteristics or flow or time of a menstrual cycle for reasons like
Hormonal imbalance, medicines, other ailments etc.
So, I would suggest that you need not to worry about anything and you should visit a Gynecologist for sure if this thing keeps happening again for next 2-3 cycles.
Thanks for Trusting & Posting your Query on this forum.
Hope this will help you. Feel free to ask any further question.
Have a nice Day.
Regards,
Dr.Abhijeet