Let us read together Genesis 21:1-2:” Now the LORD was gracious to Sarah as he had said, and the LORD did for Sarah what he had promised. 2 Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him."
One thing that we learn from the extract is that God is faithful and He keeps His promises. Maybe we want Him to be faithful and grant our wishes, but that is not the case. He is not obliged to fulfill all our dreams and desires. He obliges Himself to Himself and His word. He is perfect. And He is good. So, if you believe Bible, you should also believe the promises that are there and trusts that God will do for you what He has promised to. Good luck in keeping your faith!