Haven't got my period

I have been on the pill for over 3 years now and I had to change to a higher dose because I was bleeding through. Everything was normal but in the past 5 months I haven't gotten my period. I have been taking the sugar pills so that I get it but nothing happened. I thought I was pregnant but blood tests came back as negative. Was wondering if anyone has had this problem? I recently had some spotting but that was when I was on the hormone pills and I'm not meant to get my period for another 2 weeks