Why can't I get pregnant again I am 41 and I have 2 childrens, I haven't gotting pregnant in over 21 years.

Time for consult. If you have been having unprotected sex with your partner for years & not conceived, a workup at a fertility center may be the best way to find answers. Both you & your partner will need to be evaluated. Your regular OB can sometimes start the process but the center can study you both & provide information on assisted pregnancy if needed.
When . When you are 20 years old, the eggs in your ovaries are likely to be healthy. Those eggs age over time. By the time women hit 40 years old, fertility rates drop markedly. In your 40's there is also a much higher chance, that if you do become pregnant, that the baby will have a chromosome abnormality.