How?! OPKs were totally wrong? And a period?

I've had really light and rather short periods since I came off the pill and my cycle mostly stabilized. I stopped using OPKs after my last cycle. I had my period, it came a few days early, but still.

Two days ago I started lightly spotting, after I had felt ovulation pain three days ago. Last night the spotting was a bit heavier, I had a sore back, my boobs ached and I was moooooody! I thought my cycle was messed up and I was getting my period super early.

Just our of curiosity, I took a test this morning. Easy@home came up immediately and Clearblue says I'm 2-3 weeks. But look at my calendar. How is that possible?! (I'm not mad about it, don't get me wrong! I'm just very confused.)