Hello and welcome to HCM.
Thank you for your query.
I have gone through your query, and as per textbook knowledge an
implantation bleed, with or without conception should occur about a week before your period. But, this theory is well challenged, as it can also depend on the date of conception.
Although your symptoms are in relation to a change in hormones, this change in hormone levels could be the result of a
pregnancy, or even just a period (which you did experience) although irregular. As your menstrual history has been regular throughout, the chances of a pregnancy do increase.
In my opinion, we should first have to rule out a pregnancy, which can be done with the help of a home pregnancy test conducted at least 2 weeks after the date of conception, using an early morning urine sample, which would be most concentrated and yield a most accurate result. You might have to repeat this 2-3 times to get a confirmed result.
If pregnancy has been ruled out, I would advise you to wait till your next period and see if the period is irregular once again. If it is normal, try not to pay too much attention to the last one, but if it is irregular again, then it would be wise to visit your doctor and discuss the scenario. Information like the use of birth control, etc; help greatly in finding the cause for such an occurrence.
I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications at: http://doctor.healthcaremagic.com/doctors/dr-shoaib-khan/64581 . I would gladly help you.
Best wishes.