My stools are very hard suddenly?

Evaluation/diet. Look into your diet-you may have change your diet some way that is affecting your bowel. Your diet may lack fiber, or you may dring less water that normally. , or under some stress.Stress does affect your bowel as well. If you do not have any of the above reason, then you need to see a doctor for evaluation.
Hard STOOL. Hard stools are caused usually by change in diet or certain medications and not drinking enough fluids.I would suggest you use over the counter stool softner like docusate sodium and drink more water, and change your diet tio include vegetables, whole grains, legunesfresh fruits.That you change your stools from hard to soft.If all that does not help then see youe doctor.