Hard to get pregnant after first baby?

Veronicuhhhh✨
It seems like our first son happened so quickly, no trouble with getting pregnant especially because we weren't planning it... but now that we're trying for a second baby it seems so hard to get pregnant. I've never been diagnosed with anything detrimental to conceiving which is why I'm stunned. Usually my periods are never late/ never early. Except in march it was early and now April it's 15 days early. I'm starting to give up hope. Has anyone on here ever been diagnosed with something that would make you infertile, I.E endo, or pcos, AFTER having your first baby? I'm going to go see my OB/GYN and maybe she can give me some answers. In the meantime maybe some of you ladies can give me some advice/share your stories