what digitalrain said about water- vs. fat-soluable vitamins is true. there's a big difference between the two kinds. it's almost impossible to OD on the amount of water soluable vitamins that most of us here take. i like to say, "if we're taking too much, we probably have the most expensive pee on the net!"
the problem that i have with some doctors is that they don't know much about vitamins. so they'll tell you what the RDA is, but they themselves have done little research. vitamins aren't considered to be a part of "traditional" medicine in this country. it's funny because so many of them are quick to hand out medicine with known side effects without batting an eye. i'm not saying to not seek medical advice. i'm just saying to also ask your doctor what kind of research they've done on vitamins.
i rely on my online research moreso than anything else. it usually takes alot for me to even add another vitamin to my regime. my experience with them has been pretty positive. i've been taking basically the same ones for over two years without any problems.
i think the most important things to remember when taking vitamins are:
• do your own research no matter what you read on the board. some vitamins may interfere with medicines you may be taking. some may aggravate medical conditions. some shouldn't be taken when pregnant, etc. so check based on your own personal health. ya know?
• to introduce them to your system one at a time to see how your body will react. i like to give it at least two weeks before adding something else. if it doesn't agree with you, you should know within that amount of time, if not sooner.
if you want to try vitamins again, DEFINITELY stop taking them all for a while until your system gets back to normal. then start again one at a time so you can identify which is the culprit.
good luck!