I always O late on clomid. I don't get my +opk until like CD 18-20 and I know many others who do the same thing. Relax and try not to worry about it. You have plenty of time for that 2nd line to show up.
hi there. You could be ovulating later this cycle. Sometimes, stress will do that to you. It's also a good idea to test 2x a day, so you don't happen to miss when your surging.
Goodluck to you and yes definitely some yoga will help with the stress;)