Positive OPK right after period?

Hi everyone. A little background...had AF August 20-23. Around Sept 10, my breasts got huge (stretch marks and all) and were extremely sore/nipples darkened. I also got bad acne out of nowhere. Was sure I was pregnant. I also never get pms symptoms. I started spotting on sept 19 (AF was due on sept 22). This was dark brown and lasted about 4 days on and off. My stomach has had light cramping the last 5 days and is easing up today.  I took a opk test strip today and it was very obviously positive. Is this normal to ovulate a week after period? Or could something else be going on?