Pregnant or nah?

I'm about a week late. The latest I've ever been is like 2 days maybe 3. Now a lot has happened in the past couple weeks. My boyfriends sister lived with us for a few weeks and our bodies tried to sync so she was early and I was late but not by much but now she's gone. I took a day after pill last week when we had unprotected sex but it wasn't our first time having unprotected and I know it won't work if you're already pregnant. I threw up maybe a week and a half ago and I thought it was because I drank too much the night before but ivenever thrown up from being drunk. I did take a pregnancy test this morning and it said negative but I didn't know if it was too soon to tell or not. I'm very tiny. I'm only 110 pounds and 5'7 so I dont know if that can have anything to do with it too. I just don't know what I should do...