Constipation why oh why?

For the past 2 months I've had constipation every day. My belly gets bloated and distended and I'm not hungry very often. I switched my diet but that hasn't helped at all. Every time I try to poop it only comes out as pebbles and I still feel like there's more in there that should come out. Any idea why this is happening? And why it's been happening for so long? Thanks for your answers.