Can constipation cause nausea?

I am severely constipated. My stomache feels tight, and it feels like I need to go to the bathroom, but I can't. I have irritable bowel syndrome, and I have had constipation problems for years, but this time nothing seems to clear me completely out. I have tried benefiber, Miralax, Milk of magniuesa (do not know how to spell it), enemas, coffee, hot chocolate, foods with fiber in them, etc. It will make me go alittle after trying each of these things, but I am still very backed up, and I still feel nausea like I need to throw up.