Nausea Returning at 11 Weeks?

Hello! This is my first pregnancy and I don't really know what to expect as a result. Around 5 weeks, the "morning" sickness started and it waned around 9 weeks. I'm in week 11 now and it is back with a vengeance. Anyone else experience this? I thought it was supposed to disappear for good around the end of the first trimester...