Previous pregnancies now nothing

Hi, I have had two children very easily. I conceived the first within 3 months of trying ( I was 21) and my second was conceived in 3 weeks ( I was 24). Now ttc my 3rd ( I'm 29) and it feels like it will never happen. Has his happened to anyone else?  Does my age have something to do with it? Or could there be something wrong with me? Should I consult a doctor since this doesn't seem normal for me?