A husband cannot have intercourse with his wife in the vagina when she is menstruating or in nifas. But he can be intimate by kissing, embracing, touching etc., parts that are above the navel and below the knee. Scholars differed on being intimate with regard to the area between the navel and the knee, apart from the front or back passage.

If you mistakenly thought your period ended, did ghusl, had intercourse, then bleeding resumed, there is no sin if purity signs were observed. Once bleeding resumes, the rulings of menstruation apply, including abstaining from prayer and intercourse.

There is no need to do ghusl because of this discharge, and it does not affect the fast. With regard to prayer, wudu must be done for each prayer after the time for the prayer has begun, if the flow is continual.

A person who suffers from urinary incontinence and constant wind should do wudu at the time of each prayer, and pray as much as he likes with that wudu until the time for the next prayer begins.

Sex during periods is prohibited not just because of the blood, rather it is for many reasons as stated in the detailed answer below.