2 tests... 1-not pregnant. 2-sure there's a faint line...

Lauren
So I took a test(first response) this morning and I'm sure there was a faint line(positive) but then I took another this afternoon (clear blue digital) and it said "not pregnant". Any ideas ladies? I'm 3 days late as it is, having weird cramps but definatley not period cramps, and I can't stop going for a wee(I know not nice)