Hello,
Genes and hormones are the major factors which are responsible for the growth of a beard. Unless you suffer from a hormonal imbalance, generally there is no medical treatment available to increase beard growth. Some people may develop fully-mature beard growth in the teen years, while others may not do so until their late twenties. Apply olive oil and take some vitamin supplements for some days. Also eat a healthy, nutritious diet and drink plenty of fluids. If the symptoms persist then please consult an endocrinologist/trichologist.
Hope it helps. Take care and please do keep me posted on how you are doing. Warm regards.