Mommy's of twins!

Hi! I'm 6w 5days n I was wondering when you knew/suspected you were having twins? I never thought I was or had the suspicion until my sister told me today that I might have them since our mother had twins while she was pregnant with me, unfortunately she lost the second baby n I was born a few months later, healthy but small, so twins run in my family just not living twins, I've felt n been having morning sickness since towards the end of my 4th week, didn't get a positive test until 5-6 days after my missed period, throwing up once in the morning, sometimes twice after eating something that doesn't agree with my stomach, boob tenderness is mild, I don't notice it unless i lay on my stomach, i itch one of them or one of my nieces pinch my chest or throw themselves against me, headaches, frequent urination, tiredness. Thank you for any advice!