My periods are always a few days early. Why could this be? What could I do to reduce the number and severity of my periods?

Birth control . A cycle every 21-35 days is considered normal. Lots of patients use various hormonal birth control methods for cycle control. Mirena (levonorgestrel) iud can even eliminate it in some. For those that prefer to avoid hormones Lysteda is a new drug that works well.
This is not uncommon. The typical number of days between periods is 21 to 30 days. Some women are so predictable, that they always have exactly the same # of days between start of each period. Most women are a little less exact/predictable. If you are stressed or ill or losing weight, this can also cause irregular periods. Call your md if you dont have periods at least every 3 months or a period lasts > 10 days.
Normal variation. The first part of the menstrual cycle is called the follicular phase and it's variable in length. This is when a cyst forms in the ovary, the cyst will eventually burst and release the egg cell - that is ovulation. The simplest way to fix the period length and number of periods, is to go on birth control pills (even if you don't need contraception).
Likely normal. This could be entirely normal for you. So long as this is when your periods normally occur and there has not been a recent change, i would not worry about it too much. As for decreasing the number and severity of your periods. You could go on birth control. There are a multitude of types, so it is best to discuss this with your ob/gyn.