Trying for a baby after 5 years

I got married when I was 21. I had my first child, a daughter when I was 20 but was adopted by my one of my relatives since newborn because they told me, "You're too young to be a mother." Another obvious reason was because they didn't like the man of my choice, they said he do not have a future and so... I married him, anyways. Cut ties and started a new life, a tough one in the beginning. We had a son, a month after our marriage and then a daughter, the next year. One year apart. Trust me, the last daughter wasn't planned and we almost gave up for an adoption. I emailed the adoption centre myself but I changed my mind when she was born, the moment she smiled at me. Fast forward, years passed and we're almost 30 now and we began to try for the last child. I missed having a newborn and I sent my kids to private school, tbh, we made it. My husband got promoted lot of times, we're very stable now. I decided to have one more child before I tie my tubes. I do not want a child after 30 years old but... negative. When I was younger, it's so easy to get pregnant. Is there something wrong with me or it's just in my head? I felt like I suddenly can't conceive.