I'm a little confused, because I had an experience last night that seemed a lot like a miscarriage, but there were a lot of things that made it kind of weird that I would have been pregnant in the first place. I have polycystic ovarian syndrome. I've only had about 3 periods on my own in my life, and a little spotting. A couple of the periods had some pain involved, but nothing compared to what I felt last night. I've been having stomach upset feelings for about 2 weeks straight so I thought I had just eaten something icky or it was just the same thing that had been happening, but then it started getting worse and lasted for about 5 hours. It was like I was a little nauseous, but didn't want to throw up or have diherrea, it was just horrible pain in the middle of my stomach. It was so bad I could barely walk and wanted to cry for some of it. I took some ibprofin and it finally went away, I don't know it if was coincidence or the medicine.
Then when I woke up in the morning, I noticed I was bleeding like crazy, more than ever before. It started sometime during the night.
The weird thing is that my boyfriend and I have been using condoms and birth control. However, there's still a chance that I could have been pregnant because his cat ate half of one of my pills and got them out of order, and he's been going in without a condom but pulling out before ejaculation.
Does this sound like a miscarriage? Or just some drastic period? Is there any way to tell?

I'm thinking more now that it was just really bad cramps cause I got them again later today. It confused me though cause I'm hardly used to having periods at all. I don't know.

Have you taken a pregnancy test? If you were having a miscarriage you need to be seen by a doctor. I would take a pregnancy test just in case.