Irregular period and pregnancy test

Hi, so I have very irregular periods, so when do I take a pregnancy test for results because I’ve been taking tests they all come out negative and I last done it 3 months ago and still no period. How else can I find out I’m pregnant, without going to the doctors? Recently my left side belly buttons been hurting and it says that happens when pregnant and also happens If you’ve got any problems there. I don’t want to go doctors and don’t want my parents knowing. Is there anything else I can do. My last period was 100 days ago