Negative test

Im 17 days late. Took 4 pregnancy test last week. I did first response and an off brand from CVS. Ive been late before only once since i got off BC two years ago. I currently have 3 kids. Is it completely normal to skip a period when you never have before other then pregnancy? Ive had a lot of stress over past 4 months so could be that. Doctor isnt an option right now as my insurance is ending soon. Any insight?