All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Know, dear sister, that your question is somewhat ambiguous, and it involves several matters.
We think that you are asking about the discharge of blood when having intercourse the third time, whether it is menstrual blood because it coincided with the time of your menstrual cycle or is it bleeding due to intercourse; if this is what you are asking about, then if the discharge of blood lasts for one day and one night – which is the minimum time period of menstruation – then it is considered menstrual blood, because it is blood in the time of possibility and is not less than the minimum period of menstruation, so it is judged that it is menstrual blood, and you do not have to do Ghusl due to sexual intercourse. It is sufficient for you to do one Ghusl when you become pure from menses, and it will be Ghusl for both menstruation and Janabah (state of sexual defilement).
Ibn Qudamah said in al-Mughni:
“If a menstruating woman is in a state of Janabah, she is not obliged to perform Ghusl until her menses stop. This is explicitly stated by Imam Ahmad, and it is the view of Ishaq. This is because Ghusl does not benefit any of the rulings, so if she performs Ghusl for Janabah during the time of her menstruation, her Ghusl is valid, and the ruling on Janabah is removed. This is explicitly stated by Ahmed.” [End of quote]
But if the bleeding is interrupted for less than one day and one night, it is not considered menstrual blood because the least menstruation in the view of the majority of the scholars is one day and one night. So, you are considered pure in this case, and you must perform Ghusl due to Janabah for prayer.
If what you are asking about is other than what we understood, then please clarify to us in a clear and unambiguous manner so that we can answer you accordingly.
For more benefit on the difference between monthly menses and bleeding outside the monthly menses, please refer to Fatawa 129256, 199375, 192925, 183343, 154565 and 145201.
For more benefit on Istihadhah and irregular menses, please refer to Fatawa 345745, 380429, 362518, 145201, 326818 and 156775.
For more benefit on irregular menses and signs of end of menses, please refer to Fatawa 395488, 361450, 355546, 323464 and 231715.
For more benefit on the minimum period of purity between two menses, and maximum period of purity, please refer to Fatawa 98693, 129256, 129266, 156775 and 326818.
Allah knows best.