What is an enema? constipation? how does it work exactly?17 weeks pregnant! answers please!?

Ok you probably read both of my previous questions so I am going to the hospital cause I can't stand the pain if they do that will the give me pain medicin?? So ot won't hurt? Some one said something about watter shooting into my rectum to make the ppop come out does that hurt? And allso some one said if that doesn't work they will put a glove on and dig the crap out and I know that will hurt so will I get pain medicin for that?