throw up yellow

hello i'm 17 years old & this morning i threw up bright yellow water it was  a little thick, more watery. i did have sex using the withdrawal method a couple times, but i just got off my period like 3 days ago so i don't think i'm pregnant. i don't feel sick at all i just woke up & threw up out of nowhere w out feeling nauseous basically. is this normal for me? the throw up looked very weird, i def did not eat something bright yellow.