This is not an uncommon situation. Publication success depends on skill and, unfortunately, luck.
I've seen highly talented students struggling to publish while less skilled students seem to get handed projects on a plate and fire out papers regularly. It's frustrating, but remember that you may have been given tougher projects because your supervisor trusts your ability to complete them. Sometimes you just have to be patient - some projects take 6 months, others might take a couple of years, and some will never go anywhere. That's the nature of research. Take pride in your own work, keep the quality high and avoid the temptation to measure yourself against others at such an early stage of your career. Stay motivated and discuss your chemistry with your colleagues as much as possible - the papers will come.