Since your age is 18yrs, it is quite difficult to increase now. However, you should talk to your endocrinologist Doctor for his/her opinion. Apart from that go for some yogasana like Bhujangasana, Tadasana, Suryanamaskar, Matsyasana etc. So far diet therapy is concerned your diet should be rich in Protein,
Calcium and Vit D. For this talk to your Nutritionist for customised diet.
Next Steps
Contact to Endocrinologist. Practice Yogasana. Talk to a Nutritionist.
Health Tips
All three may be useful for your concern.