Morning sickness back!

Hey, I'm currently nearly 13 weeks pregnant. I have had morning sickness (24/7 nausea) from 6 weeks to 10/11. After 11weeks, it seemed to be gone apart from the nighttime which was great but now since 12 weeks, it's come back again with a vengeance. So basically it went away for one week and is now back again. Has anyone has this? Or know why this is happening? I really thought it was getting better and alot of people said it would begin to get better around 12 weeks but it doesn't seem that way. Ugh!