Day 45 of 34day cycle bfn :(

well I'm off to the doctor tomorrow to see what's up. All my cheap internet pregnancy tests have been negative and I am almost two weeks late now. I'm not stressed or had any big changes that would upset my cycle. My periods have been fairly regular since I had my mirena removed in march. We are trying to concieve. any ideas what could be up? anything in particular i should ask the doctor about?