Vitamins can't give you pregnancy symptoms. If you take a vitamin at the wrong time, or on an empty stomach, it can make you nauseous, or throw up, but no other side effects happen.
The box of vitamins (depending on which one) tell you to start taking them before you even fall pregnant, so good on you for starting now. I'm 28 weeks, and haven't been taking them for about 2 weeks, because everything i eat is giving me heartburn for the moment. (bad girl!)
Your breasts hurting sound like it could be pregnant, although it is a symptom of a cycle starting for some people.
I've never heard of an ache being a pregnancy symptom, but cramps, and a tugging feeling, or feeling like you've got gas is a symptom.
If you only concieved a week ago, it'd be best to wait another week, or until your period is due to take a test.
The chance of getting a negative this early are pretty high.
If you get a really light spotting, pink or brown in colour, that's not like your normal period, it could be an implantation bleed. When that goes away, test then. But then again, you may not experience the bleed.
Good luck. I hope you get the answers you are looking for.