So I'm getting super dark opk lines for almost 3 weeks now and but nothing on a hpt. I had light spotting 13dpo (sept 24th) and I'm a week late. I also had yellowish snot like cm for 2 days after the spotting and now it's ewcm and has been for 2 weeks. But Every time I take a hpt it's negative!!! I've been having light cramping and back pain and bloating. Not unusual right before my period but I've never had a DARK opk for 3 weeks straight. Could it be detecting something a hpt can't just yet?