Period after baby

Samantha • I am me.
So my son is almost five months and I got my first period 3 months after his birth and I'm just wondering does go it go back to normal or does it stay irregular for a while I'm asking because my last period was Aug 25 and I haven't gotten it back since I'm 18 days late and I'm really worried cause I don't know jf ineed to take a test (pregnancy)