Hello Deepak
you have raised interesting question.
Getting erected by mere sight or thought of a girl is normal thing in younger age. And you are not able to distract yourself form this thought after getting erection. This can be managed with distraction techniques eg giving painful stimuli to yourself on getting erection- May be helpful.

Compulsive masturbation is disturbing as causing difficulty in day to day activity. But unlikely to cause any physical adverse consequences. Semen is being produced in our body all the time. Losing semen does no have any scientifically proven adverse consequences.

Hope this answer your quarries.