Braxton hicks contractions at 18 weeks ?

This is my first pregnancy so I have no idea what to expect but the past couple days I've been having cripling back pain and a lot of discharge but lastnite was the worst I felt my stomach and by my pubic bone tightening and then releasing all night couldn't sleep my thighs and legs hurt and I woke this morning feeling so nauseous ! Has anyone ever had this ? Should I go to th E.R.?