late, but negative pregnancy test


ok i need some advic, help, anything. I am 16 days late for my period. I'm 28 years old and I have a 4 year old who has cp. I had a very difficult pregnancy with him in fact i have birth to him at 7 months. I always had irregular periods, but i mean maybe 2 times a month or extremely heavy period. never late. I was on pretty much every form of birth control besides the iud. From after my son was born til about last march. i was having really bad side effects on them. Since then me and my husband have been sticking with the "pull out" method. Now I'm a little over 2 weeks late for my period, I took a pregnancy test the digital clear blue one and it was negative. any advice, anything at all? Thank you in advance