how long should I wait to take a pregnancy test?

start a week after your missed cycle.

the problem is I don't have a regular cycle

I didn't have a regular cycle either. I basically had to take a chance whenever I thought I missed it. my cycles were basically from 33-40 so I took a chance after 40 and that's when I got my positive. I waited that long since I didn't know when I was suppose to start. @futurewilson18

just chance it.. that's really all I can say..

well my last cycle was Dec. 18th

I took mine 4 weeks after when I was supposed to get my period

I agree take a chance if it comes out negative and you still don't get a period take a test in a week or two. @futurewilson18