I'm 22.5 weeks, and for the last 3 weeks or so I have random sick moments (which usually result in me vomiting). I find though these moments pass much quicker then my first tri morning sickness (I was sick 24/7 then, with no relief at all), where as now I get nauseous and usually vomit within 20 minutes of feeling sick, then go right back to normal. I haven't been able to pinpoint if there is a specific cause of this though, like eating, or lack of sleep, or over heating.