Late period or just cycle changing?

[tinyroses72.livejournal.com]

Hi
I have had a fairly regular period the last year. It usually comes at the end of each month, like the 25th on and last 3 or 4 days. Last month it came on the 22nd. Now in the month of June it still hasn't come yet, and I wokeup today on July 1st still waiting! Also, there has been at least one month where my period came late like this and lasted 3 days, then at the end of the same month I got my period again for that month. To add, I've been very stressed out, and my entire sleep schedule has been off. I've been staying up almost every night until 4 am sometimes later (ive been having really bad sleep problems). I'm not sure if any of this means it could just be late or my stress could change it. I'm going to buy a pregnancy test today to be safe.