Tender breasts are a common sign of pregnancy, but they can occur for other reasons too - some women get them every month. If both your test were negative it's very unlikely that you're pregnant, unless there was a mistake in the way they were administered. This list of symptoms may help you decide whether you need further checks. All the best.
If your only 4 days late it could be to early to read on a pregnancy test I would go to your doctors and take a test, leave it for a week your doctor can also advise you on the best ways to conceive . Good luck