How early can morning sickness start?

I'm about 5 or 6 dpo and felt sick when I was brushing my teeth this morning. Kept gagging in the bathroom feeling like I was going to throw up. I went and got me food and I feel like I'm starving and I still don't feel good. Don't want to get my hopes up. Been ttc for a while now. Husband told me it could be morning sickness. What's the earliest anyone has experienced this before?!