Hey, I Have Been Having This Problem For A While

Hey, I have been having this problem for a while now and just decided to ask someone now. For years now I would feel nauseated before I have a bowel movement but when I go to have a bowel movement it doesn't seem to want to come out. If it does drag on to me for a long time I feel sick to the point I actually do start vomiting! Please help? Is it my diet? Do I have IBS? Or am I constipated a lot?