Are Irregular Periods And Spotting Between Periods Normal While On Cerazette?

Hi, may I answer your health queries right now ? Please type your query here...ive been on cerazette mini pill for almost 4 months. For the first 2months months my period was regular and no spotting between periods..But over the last 2months my period has arrived and a couple of days later ive started spotting which can last up to 3 weeks...Is this normal?