Pregnancy Test

Hadley • 18. Engaged. TTC.
Me and my SO have sex almost every day. We are TTC for about a year and a half now. I get over excited and want to test like the very next day (I know, it doesn't work like that!) I hear all different things; wait a week after sex. Wait 2 weeks. Wai a month? What do you think? How long should I wait o take a test? 
Note; I have VERY irregular periods, so I never really know when I've missed it or not.