positive line on pregnancy test that disappeared??

Ni
Not been feeling myself the last couple of days and also felt sick have been trying for a baby for a year now this will be my 3rd, so I decided to do a test 3 days early my test showed up quite clear with the second positive line then when I went to look at it 10mins later it had disappeared?? Am I pregnant or not I have been getting stomach cramps tonight but wondering if I'm just getting myself at it?