Please help my lmp was april 9th i didn't think i could have kids my periods where irregular i found out on july 18 i was 12 week when did i conceive?

10 weeks earlier: If you were 12 weeks pregnant on 7/18, you conceived 10 weeks earlier or about 5/9. Even with irregular periods most women ovulate some so pregnancy is always possible. By convention we count weeks of pregnancy from last menstrual period which is about 2 weeks before conception. This doesn't necessarily work with irregular periods but the ultrasound doesn't go by periods. It measures fetal size.

From US...: Given gestational age of 12 weeks on July 18th, sex for conception likely occurred 5/5-5/10. Given your irregular cycles the LMP isn't reliable to use. Good luck.