I m 44, having 4 kids, 22--20--18--15. Having dub for 2 years. Today soft tissue a bit bigger is passed along menstrual bleed, I m worried what it is?

See detailed answer. Likely you passed a intact part of your uterine lining called a decidual cast. Other possibilities are menstrual variation, abnormal pregnancy(do a test if you are worried), or some other problem with your uterus as you have had problems for a while. You should visit your gynecologist.