Late and unsure due to breadtfeeding

Hello. I have a 15 month old and still breastfeeding at bed time. I got my cycle back 7 months ago. I am 4 days late and unsure if I'm just not regular yet from the pregnancy or what. I took a test when I was a day late and it said negative. Any ideas? I plan on getting another test tomorrow so I'll have to wait till Wednesday to take it.