Pregnant

So I'm trying to avoid getting pregnant. I came off the pill as it was making me miserable etc and I've been using this app to see when I'm most fertile. Thing is myself and my partner had unprotected sex about 4/5 days before my fertile period. We had no condoms so we only had penetration for a short while before we did other things. Now I'm 3 days late. Did a test this morning and I didn't even have to wait the 3 minutes before the line appeared in the window. I can't afford another realistically and I have an 18 month old and I'm not sure I could cope with a 2 year old and a newborn