Hello and welcome to HCM. Thank you for your query. As you have mentioned a history of irregular cycles, this should not be very alarming, although a delay of 10-15 days is quite a long period. So let us look into, the possible causes. First of all, I would request you to repeat a pregnancy test, although you have done this twice. This time, make sure you conduct the test with an early morning urine sample, as this would be most accurate. It has been more than 20 days since you have had intercourse, which is why, if you are pregnant, and early morning urine sample should contain sufficient amount of beta-hCG to return a positive result. Once pregnancy is ruled out we can more forward, looking into other possible causes. Coming to your symptoms, although lower back cramps can be a sign of an approaching period, vaginal discharge is not. I would have preferred you to mention the color, consistency, smell, etc; of the discharge. As this can be a sign of an infection, and infections are one of the most common causes of a delayed period. I request you to either write back to me or consult a gynecologist to rule out/diagnose this infection. In the meantime, please abstain from all forms of sexual contact. 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. I would gladly help you. Best wishes.