Don't trust clear blue tests unless it's the digi one. I had lines on 50% of the ones I took last month, but they were false +. I could see some of the lines from across the room they were so clear. Never got a line on anything else though, and af came right on time.
I would go and get a first response or a superdrug test, they are supposed to be pretty sensitive, and unlike clear blue they don't give false hope.