I can't poop D: Help?!?

This is probably incredibly TMI but I'm starting to panic here so I'm going to ask anyway. I haven't been able to poop for the past three or four days. The last time I did before that, it was extremely difficult as well; I was in the bathroom for literally hours and when it did come out, it was just in these hard little pellet-like things. I don't usually have totally regular bowel movements though, I go about every two days but they're always normal. This evening I ate an apple, a FiberOne bar, and a prune; I did have an ample amount of fettucine alfredo earlier though so I'm not sure whether that might have been unhelpful. xD When I try to ~go~, I know there's *something* right there but I can't seem to push it out, maybe because it's too hard or too large. I took a stool softener but I'm not sure if that'd help if it's already right there. I'm terrified that it's an impaction or something and I'm really starting to freak out. Is there anything I can do to help?