I don't know Becky, I think that you might have a good chance of ovulating before the 28th. That's two weeks away and if it was your period, then you would hopefully be ovulating around 2 weeks after that.
I would just say to keep using the ovulation tests just to see if you get a positive...I know they can get expensive, but it could be so worth it.
I think you got a shot at it before Robbie leaves. Just a question...what is OH stand for???