Thank you for your query. If your periods are regular and only in this month you are having late periods then there could be two reasons. One is you are pregnant because of unprotected sex with your partner, you also mentioned that the pregnancy test is negative, but did not mention when you did it. Generally pregnancy test gives result on pregnancy status if done between 7 to 10 days past the expected menstrual cycle date. Since you also mentioned that the period was scanty and only lasted for a day it is advisable that you repeat the home pregnancy test after 2-4 days to confirm whether you are pregnant or not. Sometimes irregularity in periods and scanty flow could also be due to stress or strain, exercising heavily, dieting etc.
However abdominal pain, back pain and sore breasts are common symptoms for both premenstrual cycle as well as for the early pregnancy. Since each individual has different symptoms it is difficult to conclude based on symptoms.
Hope that answers your query.
Have a good day.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.