I had light pink spotting only during wiping. What could this be? ?

I've had irregular periods for awhile. I had one Oct 1-5, Nov 3-8, skipped Dec, �Jan 20-23, Feb 16-23, skipped March and Apr 5-10. In May on the 17th - 20th I had light pink spotting only when I wiped. I wouldn't even call it spotting. I wore a pad and sometimes it would stain it but not often. I was sexually active on May 9th. We didn't use a condom but we used the pull out method. On May 20th, the last day of this spotting we were intimate but he didn't pull out. We were intimate again on June 5th and yet again he did not pull out. What are the chances of being pregnant before the spotting and what are the chances of getting pregnant now, after May 20th and June 5th. I have no idea when I ovulate because of this weird spotting. The first day of my last period was April 5th and lasted through April 10th.