Well the funny thing is that a lot of premenstral symptoms resemble pregnancy. The only 2 really tell tale symptoms of pregnancy is a absence of a period and a positive pregnancy test.
Because you don't have a regular cycle "I'm always late," I would try to relax and give it a couple more days. The pregnancy tests that are out there usually can test correctly 3 days after a missed period. It is possible to get a "false" positive. Good luck to you. I hope some of this was helpful.