To address this question, one needs to get an idea of a baseline when it comes to figuring out if truly the hair is not growing . Keep note that hair grows at the rate of 0.5 inches / 1.25 centimeters a month.
What is your baseline?
Your baseline typically is what you would use to compare the rate at which your hair grows. First, start by doing a length check on your hair, taking sections from each part of your head and measure them. Then wait at least a couple of months before you do another measurement. At least 4 months to get a typical 2 inches of growth, if all factors are kept in check.
What is your hair routine?
Look at what you are currently doing in terms of your hair routine. Is there something that you are doing that could be hindering growth? Is your routine lacking proper moisturizing factors and maintenance processes?
How is your diet and lifestyle?
Most of the hair problems that people have stems from what they are eating. Sometimes, your diet and lifestyle habits might be affecting your health and indirectly your hair growth. Make sure that you are drinking enough water, eating the right types of foods and getting enough exercise. This will help in the circulation of blood, which helps hair growth.
Are you retaining length?
Remember, in normal cases, hair is always growing. The issue might be that you are not retaining length. If your ends are breaking off easily, you might not be doing a good job at sealing your ends. Using a thick oil or butter to seal your ends will help in reducing the breakage in that area and minimize split ends.
How often are you trimming your hair?
Although this is not a problem, many people still go by the "relaxed" way of thinking when it comes to trimming their hair. They trim on schedule, every 6 weeks.. every 8 weeks... whenever, without really thinking, does my hair need to be trimmed? Think about it this way:
You start off Month 1 with 4 inches of hair, and then 2 months later, you trim off half to an inch of hair (or more if the person trimming is scissors-happy). Then you measure your hair and it is maybe 4 and a half inches long... then you say, "My hair is not growing!!". Now, remember hair grows half an inch each month. Meaning that in 2 months you should have at most 1 inch of growth... well, in the 2 months mark, you chopped that off.. o_O see my point??
Stress, medication, health condition, some autoimmune diseases such as alopecia can also affect hair growth. If you do not see retention of growth in your hair, you can contact your health physician.