13 days late on period

Hi, my name is Katie, I am a 18 year old turning 19, I have had the IUD Paragaurd for about 3 years now but have not gotten checkups, my boyfriend and I of one year do not use protection and he uses the pulling out method. I understand it is possible to get pregnant from precum because there is sperm present, I need input because I am 13 days late on my very irregular period and I'm not sure if it is just late because of my cycle or if I should take an at home test, and if so when I should do so. Any input would really help!