In my upper body i.e in between collar bone and chest there is a deep cleavage.and in the back the bones in upper side is visible.would u please suggest?

Pectus excavatum: This suggests a congenital (birth) abnormality of a "caved in chest." this is likely not an issue now that you are 18, as most chest cavity and lung growth has been completed. All that remains is a cosmetic deformity. It can be associated with some syndromes like Marfan and spinal muscular atrophy. See a cv surgeon if you suspect heart/lung dysfunction.