When does the uterus lining start build up again and for how long it do this?

The uterus lining starts to build up again shortly after the end of a menstrual period. This process, known as the proliferative phase, lasts for about 14 days. During this time, the endometrium (the lining of the uterus) thickens and becomes increasingly vascularized (supplied with blood vessels). The glands in the endometrium also begin to produce mucus, which helps to nourish the developing embryo.

The proliferative phase ends with ovulation, which occurs when a mature egg is released from one of the ovaries. After ovulation, the endometrium continues to thicken and become more vascularized. This is in preparation for the implantation of a fertilized egg. If implantation does not occur, the endometrium will eventually break down and be shed during menstruation.