Normal to push back ov date?

Brooke

The app had me ovulating on 8/16, then it changed to 8/17, now is saying 8/18.. I realize that I am putting in neg ovulation tests, but my body and temps are telling me that I should be.. do they look like they are getting any darker? Also been slightly nauseous the last few days, anybody else get that way when they are ovulating? That’s never been the case for me.