What Causes Irregular Menstrual Cycles?

Hi, may I answer your health queries right now ? I got married an year ago. before marriage, I had regular menstrual periods. after marriage the it has been irregular and unpredictable. From the normal 30, it was 32, then 37 and now 42 days long. and every time the home pregnancy test gives negative result. Is this serious? will this hinder concieving?