OPKs picking up hcg??

Hannah • -Jeremiah 29:11- Hairstylist Expecting baby #2 dec-2015!
I read online that they can pick up hcg, I took two one yesterday one today, (ran out of hpts 2 days ago and was expecting AF so didn't get more) I'm 4 days late on my period, but I started spotting brownish/pink today. I've been crampy for 6 days and all negative tests. What's happening? Should I go get an hpt even if I'm spitting? Sorry if I sound crazy, swear I'm not!