Does the bloody discharge also count as a period not to pray Salat?

I am 47 years old married woman, mother of four children. I have always had a regular menstrual cycle, but for the last three months I have a problem. I am in pre-menopausal stage and have fibroids, according to my doctor. I used to have 7 days menstruation, but now I have 8 days of slight bleeding discharge (thick without flow), which in my opinion is not really the menstrual cycle. Then I have 8-10 days of very heavy bleeding. Together it is usually 17-18 days of bloody discharge and heavy bleeding together. When should I count my cycle so I can pray Salat properly? I know that a normal period should be between minimum 3 days and maximum 10 days. Should I count from the beginning when I first see the blood, or the second time when I have very heavy bleeding? Does the bloody discharge also count as a period not to pray Salat? I cannot compare to previous cycles because they vary time to time (sometimes I have 4 weeks without any bleeding, sometimes I have only 10 days without any bleeding).