Nausea

I have no idea why, but lately I've been feeling nauseous in the mornings and today was the one day since last week it lasted all day. I know I'm not sick but morning sickness been a thing with me for a week. I'm sexually active and my period is suppose to start in 4 days. I'm experiencing symptoms like my boobs feeling tender but I usually know that's

when I'm going to start my period. Does anyone else feel nauseous before they start their period?