The balance of estrogen, progesterone, and testosterone in your body is what makes or breaks a good cycle. An imbalance in any of those hormones can mean painful periods, disruptive PMS, irregular cycles, or periods that are too heavy, too light, too frequent, or too far apart. Conditions such as fibroids, endometriosis, and ovarian cysts can develop as well.
Internal factors like nutrition, liver function, and metabolic disease can influence the balance, as can external factors, such as toxins, exogenous hormones, and stress. Chances are that several of these causes may be impacting your body at once.
The truth is that a difficult cycle is not normal, and is not just "a part of being a woman". Ditch that idea. There are effective natural treatments that may help rebalance your hormones, and may give you an easier, more manageable, and predictable cycle - as nature inteded!