Second time late in 3 months?! Anyone had this problem?

​Been trying for our first for about 8 months and normally have a 29-34 day cycle. I thought I was pregnant in December but did tests and negative so after having bad pains and some symptoms I went to the docs and got blood tests to check everything and nothing, my period finally came on day 51!. Last month was pretty normal at 34 days but today I am on day 46 as don't know what to do! I took a test last Friday but that was negative. Shall I wait until I get to 51 days again? Has anyone else had this problem? Or have you ever had a massive belly where you really do look pregnant?!? I don't understand it, was same in December that's why I thought I was but not sure if its to do with being late that the belly swells?

​Can anyone help please?