I actually started getting morning sickness about a week before I even found out I was pregnant. I thought I just had a stomach bug that wouldn't go away lol I found out around 6 weeks, so I'd say I started getting it at 5 weeks.
My first I didn't feel nauseous until about 6-7 weeks, this time I had it right at 4-5.
Everyone and each pregnancy is different. For me I started feeling it around 4 weeks this time but with my other two it was a little bit later.