Taking vitamins in excess is not going to harm your body. In fact, taking large dosages of high quality vitamins is recommended per several studies to help ward of degenerative diseases. Because Centrum isn't very high on the quality scale, your body was most likely just having a bad reaction. The best type of supplement to take is one which is pharmaceutical grade and NSF certified. Those are the best products to take and are usually guaranteed to break down in the body, unlike most over-the-counter supplements.
You can overdose on nutrients and vitamins. Taking some in large doses can actually be fatal or can cause damage.
One such case is iron intake in males, which I believe daily intake should be 8 milligrams. Overdose can cause death within a week apparently (of continuous overdose).
Some vitamins however, are fine no matter how much you take in, Vitamin C is one such example.
If you are concerned, you should look for some approved websites and see what are the Recommended Daily Values for each vitamin, check and see which of them in excess is harmful, calculate the amount you are intaking total for that specific nutrient, and judge yourself if that exceeds the limit.
Not to scare you or anything, but I don't want you to leave here with the impression of "more is good for every case", remember the cliche quote that "too much of anything (including the good) is bad for you".
Lastly, no, you just started on these vitamins correct, if there was any damage done to your body, it should not be permanent.
P.S. If I'm in the mood, when I get back to my apartments (currently visiting the fam), I'll take a look into my nutrition book and do all the RDV findings for you, just give me a list of the vitamins you wish to know more about. I could tell you what they do and the like as well.
Good point Mikolas. You can "OD" on iron and some types of Vitamin A. As for the RDV's, those do not indicate the MAX amount of a vitamin or mineral you should be taking. Rather, those were designed to fight off such diseases as scurvy or beri-beri. Classic deficiency diseases. For instance, researchers discovered that 60mg of Vitamin C would prevent people from getting scurvy, so 60mg became the RDV (or RDI). You can get 60mg of Vitamin C in 1 orange, lemon, or lime just to name a few.
Some vitamins are hard on your stomach and digestive system, always eat when you take them. Your body will absorb the vitamins you need and get rid of the excess through urination. You are okay and haven't harmed your body, just eat and take the correct dosage usage on the directions. Also, I have found a lot of vitamins to be very constipating, just take a stool softener daily and it will help.