What to do about morning sickness

I'm at week 16 of my pregnancy and I still can't stop puking. I've tried multiple different kinds of medicines and home remedies. Every medicine I take works for about a week then stops working. Home remedies are like nothing I can't keep food down and I can barely keep liquids down, including water. I've been taking unisom at night and for a week it helped so much, but starting this week it hasn't been helping at all. I'm at a loss. I'm starting to become depressed because I'm hungry and in pain from all of the puking. I can't gain weight and I watch my pregnant friends enjoy giving into their cravings.. any advice would be nice.. or at least knowing I'm not alone in this would be nice.