First time pregnancy!

Just found out Tuesday night that I'm pregnant! I'm excited but I also get that thought in my head about "what if I bleed"? My period was supposed to come Dec 3rd but never did so I'm 6 days late and still no signs. I have been have some mild cramping similar like period cramps but it feels like pressure feel and mild cramps . My sister in law who is pregnant with her second one told me today that pressure feel were normal. I can't take prenatal vitamins! They make me wanna puke! So I really don't know what to take right now until my doctor appointment which is Dec 19th. My sister in law told me to buy Flintstone vitamins because that what she tastes. I also been really sleepy and all I want to do is sleep all day plus my headaches been awful and heartburn. I just hope everything is related to the pregnancy! Once you take a pregnancy test for the first time, and it tells you your pregnant, does that always mean it's true? Just making sure before I test again? I also have a app downloaded on my phone called Baby center and it says I'm 4 weeks....just wondering if that's true!