Champix vommiting

After 5 years of heavy smoking, one week is as far as I got with cold turkey and kept finding myself buying a packet after I swore I had my "last cigarette" for what felt like the billionth time. I tried patches, lozenges and even hypnotism but nothing worked. I was always a bit wary about Champix because I have bipolar and I have heard that it can really affect your mood. I spoke to my psychiatrist and he said to give it a go and if any signs showed up to stop. I'm on my third week of champix now and have been smoke free for the past 2 weeks with no obvious changes to my mood. I did have some pretty crazy nightmares the first week, but I know take some melatonin with the night tablet to help me sleep better and it's made a difference. The only thing I'm struggling with is the nausea. It was manageable the first 2 weeks and would not last that long, but the past few days after my night tablet I get really nauseous, even with meals, and tonight I vomited. I really want to continue the course because it's actually working, but I don't if I can cope is the nausea keeps getting worse. Did anyone else have this problem or have any tips on what will help?