Dates and weeks are confusing

I had my LMP June28th and missed my period a week ago, yet I'm 5 weeks pregnant w due date April 4th?  In my head, it seems like the clock should start w ovulation (3 weeks ago) or implantation (~1 week ago).  It's so confusing.  pregnancy isn't 40 weeks at all, it's like 36 weeks, basically.  Did anyone else find this super weird?  Can you confirm that anytime they talk about pregnancy weeks they mean since last period start date?  Maybe I'm just misunderstanding.