OPK wrong?

SC
Is it possible to be ovulating but not get a positive opk? I've been testing every morning since 3 days after the end of my last period which was 4/18-4/26. Haven't gotten a positive yet. Also been checking CM, bbt and CP. CM has been watery and egg white. CP has been high, medium/soft and sorta open last 3 days. bbt is harder for me to understand but it's been somewhat constant. My period in April was messed up (I had two 11-15 and 18-26) so I'm
not sure if I just missed my window from the 11-15 period? I saw my doctor 4/26 and she told me to count the second one (18-26) but now I'm wondering if I just missed the correct dates. I'm having cramping now. If we're going off 11-15 then AF is coming Saturday. If 18-26 then AF would be coming 19th/20th. What do you girls think? HELP!