Is this a miscarriage or just a late abnormal period...??

[merryblueberries]

OK, I need help shedding some light on this... My cycles are relatively regular and my periods always pain free, with maybe a twinge that tells me my period has arrived. This one was just plain weird. I need to state that I've had unprotected sex two weeks before my period was due. I'd been feeling a bit out of it and then two days after my period was due, I started getting brown discharge (i'm guessing this is old blood) which then turned into a normal flow with clots (it never got heavy). But for the whole day, I had a terrible dull pain in my lower area that made it very hard to focus on anything else, and my breathing got a bit laboured because of it. It felt like someone had shoved razor blades up there and I had to push them out. I had a hard time sleeping too, because my lower back was aching and a pillow didn't elevate the pain. The next day, the pain had subsided but I got the worst migraine, hurt to get up and to look at anything too bright. I also felt so nauseous, I thought I might puke. I dosed up on ibuprofen which helped a bit. The morning after, (warning TMI) I discharged a piece of flesh in the shower the size of a thumb. I'm not too disgusted by this stuff so I picked it up. I know it wasn't a clot because I always get those, this was like a slice of raw beef (2 inches long and 1/2 inch thick). The next two days passed like a normal period with no pain. But I never usually get any cramps or migraines or bits of tissue falling out of me during my period so is it possible this was a miscarriage and I just didn't know I was pregnant? Do some periods look like this? I'd appreciate any info you guys could give as to what was going on.